I'm going to change my mind about a gift.
What exactly do you mean by that, to change your mind about a gift?
I am not going to give this gift to someone even though I told them I would.
If you tell someone you're going to do something, you should do it. If you don't people won't trust you in the future. You should do what you promised and give them the gift.
No I think I could get away with it.
It's not important that you could get away with it. It's that every time you go back on your word, you're less likely to have people trust you in the future.