How can I make amends with the one I wronged?

the kamma has been laid down

now there's no use in scruples over the past

the best and the most constructive thing to do i think is make a commitment to never repeat acts of callousness and actually fulfill it

it's possible to mitigate acquired new bad kamma, counterbalance it as it were, by development of wholesome qualities such as good will, cheerfulness, compassion

What you have is a ‘healthy kind of shame’, says Thanissaro Bhikkhu in his article “Living Forward, Understanding Backward”, and advises you to develop goodwill for everybody as, then it is a lot harder to harm people, harm yourself or harm anyone else.

... So a large part of the practice is learning how to take mistakes in stride. The Buddha says you should feel shame over your mistakes. But it’s not the kind of shame where you feel that you’re a horrible person, but simply realize that you did something that was beneath you, that was not appropriate for you. You don’t want to repeat that mistake. So it’s a healthy kind of shame. It’s not debilitating.

He teaches the same attitude in terms of issues of remorse. You realize that you’ve made mistakes in the past. He doesn’t have you dwell on them more than just recognizing that they were mistakes. And then you remind yourself that no matter how guilty you may feel about the mistake you made, that guilt is not going to go back and erase the mistake. The best you can do is to resolve not to repeat it. And then you try to strengthen skillful qualities in the mind. And he highly recommends the attitudes we were chanting just now—unlimited goodwill, unlimited compassion, unlimited empathetic joy or appreciation and unlimited equanimity. In other words, put yourself in a position where you can feel these emotions for anybody.

Basically you start out with goodwill. Reminding yourself there’s no need to see anybody in the world suffer, because if people are suffering that’s why they tend to do evil things. They feel threatened, they feel attacked, they feel like they are in a weak position and so they strike out. So no matter how much you may dislike a particular person, there is really no reason to wish ill on them. What you do is wish for this person to find true happiness. If they could find true happiness within, the disagreeable behavior that they’re engaging in would fall away. At the same time, if you can develop goodwill for everybody, it’s a lot harder to harm people, harm yourself or harm anyone else. It strengthens your resolve not to repeat your mistake.

You may do a chanting / convey rememberence by engaging in a charity event at a Temple. It is a good idea to talk to a Monk in the Temple and arrange a small Alms giving event at the Temple or in your house. By doing this you will be able to send collected merits over to its soul if it is in a place where it can receive. As the above person just mentioned, never repeat acts of callousness. Spread loving kindness to each and every living being from east to west, north to south and top to bottom. May the noble triple gem bless you my friend.

WHAT CAN I DO TO REMOVE PREVIOUS NEGATIVE KARMA?

Nobody likes to suffer, so we all like to rid ourselves of negative karmic potential.
There are several possibilities, and in fact we may need to try and apply all of these methods as much as we can:

• To avoid having negative thoughts that lead to negative actions in the future, we need to observe and control our own thoughts and behaviour, and destroy our negative attitudes.
• Similarly, we can observe/study (meditate) our own mind and encourage positive thoughts that lead to positive actions.
• We can avoid negative karmic seeds to ripen by purifying it, using the four powers of purification (see below). Although this does not eliminate the negative karmic actions, it can avoid the results to occur.
• Ultimately, when we realise emptiness directly (see the page on Wisdom), and remove all our delusions, we are not under the control of past karma anymore.

THE FOUR POWERS OF PURIFICATION

The purification practices found within Buddhism are not unlike the practices applied in many other religions. The most essential mental factor that one requires is sincerity or honesty with oneself. When one wants to purify past negative karma, one has to do some action with the correct motivation. This is summarised in the following Four Powers of Purification:

1. Power of the Object: One should practice thinking of all sentient beings one may have hurt. Traditionally, one remembers all sentient beings and the Three Jewels of Refuge (Buddha, Dharma and Sangha), by generating compassion for all sentient beings and taking refuge.
2. Power of Regret: This should not be senseless guilt or self-recrimination, which are said to be useless emotional torture. What is intended here is to examine oneself and one's actions and to recognise that negative actions done in the past were very unwise.
3. Power of Promise: As a logical consequence of the above, one should promise not to repeat these negative actions. It is good if one can promise to avoid a negative behaviour for a specific time, or at least promise that one will put effort in avoiding repetition. Not being honest at this stage makes the practice useless or even harmful to oneself.
4. Power of Practice: Basically any positive action with a good motivation can be used as practice. Traditionally in Buddhism, one can practice e.g. making prostrations (throwing oneself to the floor - as a means to destroy pride), making offerings (to counteract greed), reading Buddhist texts (to counteract ignorance and negative thoughts), reciting mantras etc.

Source: A View on Buddhism, BUDDHIST KARMA

The highest level of Buddhism explains it is 'ignorance' ('not-knowing') rather than 'the self' that performs hurtful actions. This is the method for the highest freedom & dropping the heavy weight of guilt.

As for the cat, I am sure the cat was also naughty because cats are often naughty. If the cat is reincarnated, it can, the same as you, learn from & improve its actions.