if you really want her back then you cant try to do something
stupid because making her jealous wont always help because then she
will think you have moved on. if you really want her back just say
you are sorry and want her back or say that you miss her or even do
the easiest thing in the world just be yourself and if that doesn't
work then maybe you aren't meant to be together.
Figure out why you lost her, and correct that.