You might want to take an even bigger leap and perhaps look at universities when you choose your GCSE options, I kinda wished my teachers told me this. If you're sure you want to do CS then see the sort of subjects they want you to take in AS and decide from that which GCSE subject will be the best for you.
Some uni's don't count Latin as a subject, but if you really love the subject continue on with it. Grades shouldn't matter so much when you are choosing your gcse's, just choose it on purely what you love and is interested in.
As for computer science, if you know you are definitely going to go into this field with no regrets then take it. Besides if you really did like latin you wouldn't have thought about taking computer science at all in the first place.