How to ask a girl out?

i really like a girl have done for a few months we go out as part of a gang i speek to her and regullary walk her home and of course all my freinds keep making little jokes about it to the girl saying i lke her and so fourth but as we was alone i told her i was just her mate but heres the thing i want to be with her so badly so how could i ask her out or get her to really like me because i think she just considers me her good freind , Please Help Thankkks