How do i stop being so anxious when the girl i like doesn't text me back quickly?

You have to try to focus on other things and remember that you had a life before this girl, even if it's hard. You'll find that the more things you have going on in your life, the less you'll worry about whether or not someone texts you back.

Well i think you should try to focus on something else like your work for example, or watch something or work out or have a conversation with other ppl.Someone once told me that a busy mind never thinks about something or someone specific, so just ignore that anxiety and try to think or do something that keeps you distracted. 

Ask yourself why you get anxious?Is it because you need affection, reassurance that you are loved? You will know.Once you understand the anxiety can be reduced.Also have other interests or hobbies that you love to do so you are not so focused on being with a girl to make everything perfect.That very rarely happens without some effort on both part and compromise.You are there yet.So slow down and take things day by day.

Mine won't even text me