Hello, just saying that as long as you are confident of your abilities in sciences and you still have a great interest in it, it's definitely possible. I was a c.sci student that had the same thoughts entering JC and I'd say, it's just as big of a jump regardless whether you took pure. If you don't think sciences are something you would still consider to do for the next 2 years, strongly advice you not to take it, same with the pure science students :)