Any advice? Friendship problems

I don’t think I’m putting enough effort into my friendships because I choose to prioritize my close friends over my other friends. I only have three close friends, and one of them has recently told me the reason I feel so lonely is because I need to start engaging more with my other friends, and it’s true. We’re on summer break and I haven’t met up with any school friends since school, only my three best friends. The only problem is that I’m afraid I’m being annoying and I don’t really know how to have a long conversation with my school friends. I just get nervous talking to them, and I think I’m making it worse by not talking to them. How do I fix this? I just can’t seem to make myself text them, I’m just too nervous.