How can I stop being so shy and approach females that are showing interest in me?

Im used to being approached so now taking on the role I still haven't gotten into it. i dress a little boyish with the baggy jeans and a fitted top, but I am no butch. Im attracted to feminine females mainly. the thing is i will see a girl giving me the eye and i just do nothing. some girl in a car was interested but she thght my friends sister was my girlfriend, when me and my friends sis were walking, her and her friends rolled up beside us. we made eye contact and all but i didnt say anything i just looked and she looked kinda guilty i guess. these guys in the back were making comments basically indicating that she had saw me and was definetly interested. i want a girl but i will never get one being so mute! lol. i might be a little flirty by smiling and giving a look but after that i dont do any type of approaching. girls tell me im cute so i shouldnt be shy but i mean come on now this isnt the straigh world...