How to prepare for undergraduate research of which I have no background in? I recently applied and got accepted to a very large research lab in the U.S. Although the catch is that I did not get put into my major ( Biology ) and instead was placed into computer science ( simulations/super computing). 

I reason this is because I had several computer science classes in the past, but I eventually changed majors to biology due to not flourishing with high level maths or coding. 

I assume that to prepare for any research, one must read the supervisor's papers and self study. Although the issue is I feel I am totally outmatched for this position, due to my struggles in computer science before. Is there a good strategy for approaching this upcoming internship or should I resign instead?
My advice is to discuss this matter directly with whoever your supervisor will be -- tell them about your past experience, your concerns, and ask for their advice. They may be able to have you shifted -- or they may tell you that they were explicitly looking for your biology background. 

As to why they would be explicitly looking for your biology backgrounds -- computer scientists frequently collaborate with other scientists when working on large-scale simulations. The reason for this is that there's two sides to the simulation -- the actual code required to run it, and the domain knowledge required to design the code in the first place. As @Sumyrda pointed out, this may be one of the goals of the internship (to give you experience in working with/as the domain expert).