Hiya!
I would say to try not to worry too much about this at the moment - it's probably best to see what grades you actually achieved first! Your perception of how an exam went is usually not that spot on, and the grade boundaries will change if everyone found the exam very difficult. Don't lose hope! You were predicted those A's for a reason
I'd say, if you do get grades lower than you were aiming for, to go and speak to your college tutor, or whoever is helping you with UCAS applications. There's a chance they will still take you on even with lower grades/predicted grades.
There are also options to go through clearing - if it gets to results day and the courses aren't filled up, then Universities often offer places to students with lower grades. I'm assuming you won't be applying for another year, but have a read of our guide to clearing
here and
here.
Hope this helps!