It sounds like your underlying problem is that you really care about what a girl thinks about you. You care if you fail, and if you "screw up".
There is no quick fix solution for this. Instead, realize that you can choose how to feel about something. If I buy a cheescake tomorow, I can either be excited about it because it will taste delicious, or I can be annoyed because it is going to fuck with my washboard abs (lol j/k, my abs are like a ninja - they're there, but you just can't bloody see them!). But if I hold that cheesecake in my hand, I can literally choose which I want to feel. And I can feel one, and then choose to feel the other.
You feelings are a conscious choice. Sure, it's not totally easy to just choose to change your emotion towards something, but it can be done. And this is what you need to do. Realize that there is no reason for you feel down and upset about these things. Just choose.
Here is an exercise for you:
1. take a pen and write how you feel when you don't get a great response / she doesn't reply / whatever
2. Write the mindset and attitude you want to have instead when that situation happens.
3. Write down the logical reasons why the mindset you want to have, is the truth.
4. When the situation happens, force yourself into the good mindset.
And good luck
