You won’t know unless you try! It is definitely possible but you will have to work hard and be focussed. Make sure you plan your revision and really work on the topic areas you are weakest in. Keep reviewing your learning and get help with those areas you are finding hardest. Make a good revision/lifestyle routine - eat, drink and sleep well, so your brain can function at its best level.
Get help from your teachers - that’s what they are there for! Regularly go to any extra revision sessions or clinics if they run them. After school, pick a topic you find hard and ask them for specific advice on the parts you don’t understand and ask for resources that will help you learn and practice those parts. Then do them. Show your work to your teacher and ask for more advice on what you have done and what you could do next. Use their help. Ask questions and get their help during lessons too. This is your learning and your Alevels, so push yourself to get the support you need. Ask and learn. Ask and learn. Ask and learn. Don’t be shy!
My daughter finds chemistry tricky but likes to ‘blurt’ to revise it. She has a large whiteboard and writes/draws everything she can remember on that topic and then reviews it after. Obviously past paper questions are excellent for all subjects, so really trying to understand the mark scheme is invaluable - you need to be able to use the vocabulary and structure that the examiners need to see to be able to give you points, so past papers and mark schemes are your best friend.
It may be a bit late for this advice but if you are still working on the curriculum, make a revision product while (or as soon as you have finished) studying a topic, so it is fresh in your mind. Then file and store that product in an organised manner so you can access it again sporadically to review, and before exams. Products like mind maps, summarising, online or physicalflash cards etc.
Good luck!