My personal recommendation would be to drop CS and to study some other A level.
If you're attracted to earning money in some IT job, then that's fantastic. As it's a great way to earn money for someone with a passion in this area.
In this case you're best off picking an in-demand IT specialisation that gets your juices flowing. And then getting training in that, getting certification in that specialisation (if appropriate), maybe generating your own experience (by doing some project for yourself or for someone else for free or nearly free), getting a starter job in that specialisation.
The best type of training will depend on you. Training can be as simple as throwing yourself in at the deep end and using manuals to discover how to do what you want to do.
If whatever specialisation you pick doesn't work out for you for whatever reason, you simply jump over to another specialisation.
For your laptop, if you're of slight build get a 13.3". 14" for medium build. 15.6" or 16" if you're built like a rugby forward.