Amended Tax Return

I just amended my tax return because I filed as "can be claimed by someone else", but it turns out that I made too much money and my dad was unable to claim me. I realize that this would have caused me not to receive the stimulus check so I am changing my filing status to say that I can't be claimed by someone else.

I finished amending and the Michigan state tax said that it could be efiled, however, every time I attempted to submit it, it failed. So I printed out both the returns to mail them. The federal return had an address and I knew it needed to be mailed, so I mailed it yesterday. Then when I read the state tax return instructions they said that the return was submitted electronically and that I should not mail a copy in. It also did not give an address to mail it. 

My question is how do I know for certain that the Michigan amended state tax return was sent or not?