I’m too insecure to have sex

So I’ve been seeing this girl for over a month, she’s the first person I’ve ever been with, we’ve only had sex once actually and when we did it, it was me who performed the act on her and i told her she can perform the act on me next time because i was not ready and she seemed very understanding and patient with me. I didn’t even take my clothes off on the first time because quite honestly i am insecure of my body. I’m a little bit bigger and i am insecure about parts of my body. I don’t like my boobs because i feel like they look weird and uneven, i also don’t like how i look naked because i have stretch marks on my body and I’m scared of vulnerability and I don’t know what to do. Although I’ve thought about how maybe I’m more of a person who gives than receives when it comes to these things. Yet I want to get over this fear but I don’t know how. I genuinely like this girl and i don’t want her to think something is wrong with her, she is very understanding and sweet and i want to be able to step out of my comfort zone to be more comfortable being vulnerable around her because i think she genuinely likes me too