I got a good first in my first year, on top of doing 25% more credits than normal (I'm advancing courses this year and the next so I get about 25% more optional modules to choose from in year 3), was treasurer of one society, social sec of another, went to volleyball twice a week and still went out about twice a week. It was very stressful at times but totally worth it, and I don't believe for one bit you should have to give up your social life/grades in favour of the other - just learn to balance them out. Sure, you might end up with 2.1 instead of a first, but think of the experience overall... you want to have fun!