What should I do? Please answer quickly?

This girl was in my class and I started liking her about the last two months left of the school year. The last day of school we walked home together and I felt like we were right for eachother. There is one problem........ She is my best friends ex. They hate eachother so I think it's ok to ask her out. I went to someones house with a bunch of people and then me her and another girl somehow got out of the group. When we were walking through the neighborhood and she was all over me. What I mean by that is I was giving her a piggy back ride ( it was awesome:) ) and she was hugging and stuff like that. So how should I ask her out? Also, my parents ask me if I like any girls and I sort've ignored them so shouldi tell them before or after I ask her out? Please answer