Am I stupid?

First of all, your not stupid.Your results DO NOT DICTATE YOUR IQ LEVEL.
I have heard of people who got 3 E's in their A Levels.

Which Uni did you get in and what were the entry requirements for the degree?

I will be studying at Birkbeck, UOL but wanted to transfer to SOAS, UOL or QMUL. I got into Birkbeck through clearing.

Do you think there is a point of me retaking these modules (only because once I finish my degree I want to get a job at a law firm) with these grades I don't think it will be possible.

Opinion?

Probably retake if you need the degree.
So, once you've retaken the exams, you get the grades you want, go to the university you want to go and get the job you want...
It's simple right?!?
If you yourself think it wont be possible, then probably retake the modules you need to.
Probably retake the B and the C....

I am studying the degree for first year THIS YEAR.

Yes, but I thought maybe if I retook the a-level exam it will be difficult for me to do well for first year LLB law.

I am gonna retake the B but I cant retake the C unfortunately because it is english lit and that subject in itself is very picky. I wanted to hopefully achieve A*AC with my retakes etc.

Whoops, misunderstood.
Okay, so you've already started uni.
It'll be a lot of work and pressure and you'd rather get a great degree tbh...
ask for advice from people who have done LLB Law, they should know better.