Fingers

I’ve never stuck anything up my vagina before. So my bf and I thought it would be a good idea to slowly try to do that. I allowed him to stick a finger up there to ease in, but it was so uncomfortable even just the slightest bit in. I don’t know how to get myself accustomed to it. I know arousal is important, but I’m honestly just super scared and kind of embarrassed that I can’t even handle a finger. It makes me super upset. How do I fix this? I want to be okay with it