Feel like joining in.
Aim for higher than a first in earlier years to build yourself a buffer. If you can go into final year with an 80% average leaving yourself only needing 60% in that year to get a first overall it takes a lot of pressure off. Also the first years are much easier, similar to AS level and A level.
Go talk to the lecturers. Seriously, it may be embarrassing if you don't understand but they want you to know. Ask them after lectures, during lectures or in their office hours. You'll feel stupid for ten seconds whilst asking but it helps so much.