Why am I so intimidated by my girlfriend?

I'm 22 and she's 21, she's had sex with 3 guys (who she was in relationships with) and I'm a virgin. I feel so intimidated by her because I have no idea how to have sex because I was raised in a strict Christian household and having and dating was considered a sin by my aunt. What do I do because I'm very intimidated by her and her sexual history. My aunt found about this and she told me, "You deserve a clean girl, not a whore who has slept with three guys." I don't want to break up with my girlfriend I love her.
Why am I so intimidated by my girlfriend?
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