Don't worry about not getting the grades to do Comp Sci at uni, I beefed my A levels hard, went back to college a few years layer and took a Level 3 Diploma in Software Engineering that I'm about to finish roughly around now and its the equivalent of 3 A* at A Level, with about 20% of the work load compared to going to Sixth Form and doing Mathematics, Computer and Chemistry which is what I was doing before.
Got my offer from Cardiff Uni for comp sci earlier in the year (which I'm deferring for casting). But yeah, I really wish someone had told me all this at the time otherwise I wouldn't have wasted two years of my life at Sixth Form.