Chances are, if you don't have AAA at the A level, Berkeley will be tough to get into.
For your gap year, get some volunteer work done, more so if it is in a leadership role. It will help with applications.
SATs are more of an equivalent to GCSE if anything, so don't pin everything on that. They'll still look at your A levels, along with taking very strong consideration of your teacher reports from school and looking at extra curriculars, essay most likely (not too sure about Berkeley specifically) and other factors.
But as I say, A levels are still important and Berekley isn't a piece of cake to get into, it's not somewhere which would best be described as a 'backup plan'!**
The SAT is an aptitude test, a cross between the TSA and GSCE maths and English. US students don't get accepted mainly on the SAT. US schools will look mainly at your UK tests, but the AS and GSCE are more important to them than to British schools. If you just got the one C and the rest of your record is really good all along, that might be less important to US schools. However, it seems unlikely you will do better applying to them.
Doubt you'll get in with AAC
But you can try if you want