How do your mock as level results compare to the real thing? Can you jump up grades even if you revised for your mocks?
Short answer: almost certainly! If you perform badly (or not as well as you'd have liked) in your mocks even though you revised, you might not be revising in a way that's effective for you, or you might just have still not done quite enough revision on some of the topics that came up in mocks. You've got plenty of time between now and the real exams to work towards a higher grade. I think it's pretty common for people's mock results to be a few grades below what they actually come out with in the end!
If you revised as much as you could, maybe try different revision techniques - practice questions, mind maps. Make sure you understand the basic stuff behind everything (particularly for science subjects eg. chemistry, physics), and go talk to your teachers about anything you're unsure on or don't understand. Go through your mock papers carefully and find what lost you marks and why you lost them, you can usually find something to work on from that