How could I relax and talk to this girl?

[2jumpsinaweek]

First I know this is what you expected EVERYONE to say, but take a deep breath and relax. I know you said you couldn't relax but try this. Talk to one of your friends before hand (a girl... if you have a girl thats just your casual friend) then find the girl you like. Talk to her in the same casual way you just talked to your other friend, look at her in the eye, smile, and laugh at her jokes. another tip is become friends with her friends. it will make you seem more casual and chill. eventually as you guys get to know each other start to say things like.
"we should hang out sometime"
or "we should catch a movie sometime"

if she says yes, and she probably will, get ready before you guys hang out. wear normal cloths, and make sure you smell alright, and then go meet her. when you guys are together still act normal, and then eventually do something like holding her hand or putting an arm around her shoulder... she might notice you like her then.
keep on going to places with her (invite other people too sometimes)
until you feel confident enough to tell her you like her, or that you want to go out with her.

Hope i helped!!!!

P.S and even if she doesn't want a romantic relationship with you, you guys still might be great friends!