I'm pretty sure I've said this before, but you really need to learn to relax.
Yes, you're eighteen. Yes, that means some legalities have chamged for you. However, you're still you. If you wouldn't have fucked it up[ yesterday, you won't fuck it up today. Conversely, if you couldn't do it yesterday, you probably still can't. That piece can be changed through effort, however.
As far as your Mom is concerned, I'm pretty sure she knows how you feel. I'm also pretty sure she knows your situation. I'm additionally sure you've helped her out with a lot of shit lately. Actions speak louder than cards on the love front, buddy.
Now, chill out and get to work on whatever you need to do today.