can i still get into a Russell group university?

for GCSE i got 1A 4B 3C and 1 Merit and recently we did a term test and i received 3A* and and A in EPQ, maths, literature and economics. I was wondering if i got really good Alevel results will my GCSE'S matter much.

GCSEs aren't important unless you are applying for a course that has a high GCSE requirement (Oxbridge, medicine and dentistry pretty much). You only need to get a minimum of B in English and Maths, and meet the requirement to do your chosen A-level course.

Most people you'll meet at RG unis have similar GCSE grade (or even much lower).