I believe you can if you are continuing with the subject to A2. I don't know about the WJEC exam board, but we were told in my college that if you weren't carrying the subject to A2 that you had to reject your grade for that exam and take whatever you got in the resit - even if it went down.
It never sounded right to me, and anyone who knows this to be not true can feel free to correct me. But that's what we were told. But it seems like you're carrying on to A2 anyway, so it's not an issue.
I believe that you will lose any money you paid for the exam though (if you did, we were made to pay for our own).