My problem is inner game. Please help me as it's driving me crazy.

I am confident but when it comes to talk to a girl I like I get nervous and my mind goes blank. I loose all my conversational ability.

Take for example last week, I was out shopping with my friend and his sister. (His sister is 10/10) and I'm very talkative, fun cos im confident.

My crush comes out of no where, taps me on my should. I'm lost for words, I start stuttering. She says a few thinks and walks off. My friends sister teases me "it's so not obvious you like her"

We see my crush again, she quickly get involved in the conversation and teases me about something. (Any other girl here the least I would do is playfully push her or banter back). Again I choke.

So how can I improve my self? This girl knows I'm confident, she has seen it, hence why she comes up to me. But I just can't do it with a girl I like.

I'm sick of going out with girls I have no interest in.

(I've given myself a plan. 4 weeks times I will ask her out, I'm going on holiday for 3 weeks, but in that time I need to find a way to be more confident with girls I like)