First, how old are you?
Second, a good bf will listen to your feelings. Even if he doesn't understand them, he will still respect your feelings. You will know if you have a good bf if you two can talk about anything, including sex, what you want during sex, how you want it, and details like that without fearing rejection.
The other thing is, to get over being nervous, practice practice practice. A speech class where I spoke to the whole class, really helped me get over my shyness. I was shy in high school and I did feel like I was asking too much of the girl by asking for sex each time I saw her on a date (about once a week). So I rarely asked.
I have a long time interest in psychology, specializing in relationship dynamics for 30 years.
(Please note, we give the best advice we can based on the information given in a post. For better advice, please include the age of all romantic partners.)