"I was going to get it" is past tense. Using past tense for something can imply that it's something that was true in the past, but not now.

This can irritate people because it comes off as trying to claim credit for intent to do the task without actually doing it.

While "Please stop. I've got this" is the best phrasing because its what your wife has requested as well as what the other commenter stated, I imagine you would have still got a fine result if you used present or future tense. "I"m getting it" or "I'll get it".

Tenses, and other grammar on their level, is definitely something you will be able to find scripts for.