is it too late to do well in my AS exams

Yes you can do it.
Last year I probably revised April to halfway through may seriously for my AS exams and got AAAA. That being said I had been consistently writing notes throughout the year.
But here we are in January, you have loads of potential. What you need to do is write brief notes on your subjects (try and reword school ones so you understand it - don’t be passive)
Start now but I’d also do like 1-2 hours when you come home from school daily to catch up on this a bit.
You clearly have got a decent memory already to have recieved those mock results with no revision, so from here on out continue to develop this when you have unit tests/essays. I’d say using active recall is the best method (try blurting everything you know of a topic on paper, then in a different pen look at your notes and correct/add in what you didn’t know).
Flashcards can also be useful for things like terminology to really drill into your head.
Use past papers when it’s closer to exams/tests. These are papers from the exam board you’ll be taking in the summer so the closest reflection of how you’ll do there.
Sometimes you can get your teachers to mark these or give you feedback, and if you are ever unsure of a topic ask your teacher!! More than likely they’ll want to help!
I know that might seem scary but it’s doable I promise. You need to set systems now (like the 1 hour after school thing), and every week write goals/to do lists of stuff you want to revise. Force yourself to be disciplined cause then it will pay off in the summer! I have faith in you - hope this helped and let me know if need anything else