Do cock rings keep you hard?

A little while back I posted about how I would go soft just before topping my boyfriend for no damn reason. The experience was mortifying and I haven't tried since. I really want to top my boyfriend but I am terrified. So, some of the comments were that I should try a cock ring. I wanted to find out if anyone had any experience with them? Do they keep you hard? At least long enough to get my dick in him haha, I think I will be good after that haha. Please can someone give me advice...