How do I get my gf to have sex with me ? She refuses to let me

Try having sex with the lights off first. It will be a smaller step for her and she might grow to appreciate her body more once she is focused on pleasure, being held and touched, caressing you, feeling each other's breath and heart beat etc instead of looking down at her stomach rolls.

Before that, start with lots and lots of clothed intimacy.

Here is what you do get lights dim put something on that gets girls hot cuddle her rub her all over tell her you love her say her name kiss her neck lips ECT. Then when shes crazy excited and hot tell her you want to lick her slight lift her shirt put her back make sure shes got a black and pillow with the temp mellow start kissing her stomach undo her pants and pull them down kiss her lower waist then over her panties and then push her legs up and panties and do your best to make her clit and puss hole feel good with your tongue.