Translation:I had not done it.
Why εγώ at the end of this sentence?
I'm fairly certain it's just for emphasis; grammatically, it doesn't need to be there.
Correct! In Greek this essentially means 'It wasn't me!'
could we have "i hadn't done it myself" ?
I had not done it. - was not accepted like correct
Could this have been written: Εγω δεν το ειχα κανει. ?
Yes. You can say it too. It means the same