Any tips on getting my academic comeback?

My A-levels
Politics (AQA) - predicted A but getting B's
Computer science (CIE) - predicted B but getting D's
Economics (AQA) - predicted A but getting C'd and D's
all judged from my progress test from November.

I have already applied to my unis and have gotten offers, but I am worried about the grades i need to achieve to actually get into my unis.
I don't have a good foundation when it comes to revising, i've tried different study methods such as flash cards, note writing, and exam questions.

The thing that worries me is where do i start off with my revision?

I didn't take year 12 serious and now i regret it as i'm really struggling with computer science as i don't really have a foundation for it.

I've been managing to revise at least 7 hours a day split between my subjects, but I feel as if i'm overloaded with work as there is so much content i need to cover. I am worried as I am running out of time as i only have around 4 months til my exam. Could anyone give me suggestions on ways to revise for my subjects? especially computer science as it is my worst subject