Nervous over sex for first time?

I ve just turned 20 and now I m in my first relationship with my girlfriend, we re both gay so sex is kinda hard to imagine as it s obviously different for us but I m still terrified of it, mostly because I m extremely body conscious and I have terrible anxiety, I m a lot bigger than she is so it s difficult to not feel awkward about being over weight and how gross I look naked, so the thought of sex is really hard for me to deal with as I ve only just gotten comfortable with her touching me in general such as her placing her hands on my arms, back ect but clothed, I still feel uneasy when she places her hands on my stomach or even my boobs but that s very rare to happen, she said to me if I would ever consider it with her and I said yes but in my head I m thinking I can t do it soon but we ve been together for months now and it s serious and I love her so much I don t want to lose her or mess it up by not being ready when she is but my anxiety is hard to deal with, so it makes this topic more difficult to handle.