how do i do this

ok, that girl that i mentioned earlier i n my last post like really likes me now, like shell talk to me whenever she gets the chance, looks at me then glances away, dittos my every move, and her body language gives it away, but one problem is she is kind of shy. On the 21st we have like a dance/dinner thing and of course I wanna ask her to it, but i think shell say no because shes shy and i know she likes me a ,ot. Im shy too, over the year ive liked other girls and when they ask me out after a while i said no, and now i think back wondering why and the girl i like now, the one ive never felt anything else like this for, she is kinda the same way as me and i need advice on how to make her less shy and feel more comfortable saying yes to me, any advice?