How do I make sure not to become this kind of person?

Just focus on that and you’re good.

There are two ways to do “bad things” 1. you’re not aware of them being bad (because you never question yourself), 2. you are aware, but you excuse them somehow.

You have already cleared 1., all you need to do now, is to remain strict with yourself to never do excuse your own bad behavior.

And to be clear, I don’t mean to constantly blame yourself, I mean “finding excuses to do the bad thing anyway, because this time is an exception”. And it’s also fine to give up on this later if you find you can’t keep it up. It would be disappointing, but any effort in this direction is good, don’t let it dominate you.