I'm studying computer science at uni and have to say you won't really have a disadvantage. Definitely not a big one. For entry they don't even ask for specific A levels, maybe just maths so you're fine with getting into the uni as long as you get good enough grades.
For what you learn at A level and what you actually do at uni, it's always assumed that you have not covered this before so it starts from scratch. For every module the lecturer will cover the basics before moving on. So while some will get it faster as they've covered it before, everyone is put on the same page before moving on.