In this situation, if you're managing to follow the course texts, you'll probably be alright.
The fact that you managed to get on the course usually indicates that they believe you're capable of doing the work - if universities took loads of undergrads who weren't capable of getting the degree then they'd never get paid. They don't educate you out of the kindness of their hearts, believe me.
I am now fully employed as an engineer having graduated from Southampton. I'm currently still doing an additional part-time MSc at Newcastle funded by my employer. Getting a 2:1 at university is a whole different ball game to getting an A at A-Level though. When I was at school, you could just learn the past papers and regurgitate them in the exam and pass. In a degree, there are an awful lot more modules where you actually have to understand what is going on, or you will fail.
Put it this way - I got nothing less than an A at GSCE, yet in one of my first exams at university I got 34%. Bit of a wake up call, that.