The first sentence is fine. In the second ‘to’ is optional. The question is whether your listener will remember the ‘to make friends’ from the previous sentence because, by itself, ‘I found it difficult at college’ wouldn’t refer to making friends. Adding ‘to’ is clearer but not necessary.
It might be even better to say:
When I was at/in college, I found it hard to. (Putting the ‘to’ at the end makes it stand out even more. You can also use ‘in’ instead of ‘at’.
It depends on how closely you think your listener is following you!