Visualization is the answer
One thing I discovered during my meditation is that almost every negative emotion felt is a result of these things I call "micro-visualizations"
Why do you feel a sudden rush of anxiety when your friend tells you to approach a hottie? Why isn't it a rush of horniness or pride?
It's because, in the back of your mind, you instantly visualize the outcome of whatever action you consider. This micro visualization sends ripples of emotion congruent with the visualization all throughout your body.
So in your case, whenever your mind considers escalating with a girl, you automatically visualize the girl recoiling or rejecting you somehow. This is the cause of your anxiety because your mind can't tell visualizations from real life. It is convinced that a negative outcome will happen.
So what's the solution? The solution is to reprogram these visualizations by collecting positive experiences or creating synthetic ones through meditation - ideally both.
That's all that social momentum is when you think about it. At the beginning of the night, you're unconfident and start thinking about all the negative outcomes of your approaches. You look at a girl and consider approaching her, but you have a micro-visualization of her rejecting you so you have a spike of anxiety.
But after you've warmed up and had a few positive interactions, you start to assume that the next interaction is going to be positive no matter which makes you more attractive and substantially increases the chance of an actual positive outcome.
So the actionable steps are:
1. Take some time every day and visualize girls reacting very positively to your escalation. What you're trying to recreate is your positive emotional reaction. Imagine how good and confident you'd feel.
I did this in-field. I'd look at a girl, consider approaching her, and hijack the negative visualization my mind would come up with and immediately switch it to a positive one, then approach. It takes some time to really see a change but it works
2. This is more powerful - push through the fear and get some positive experiences. Start small. Once you see she's not reacting as badly as you thought, really let it sink into your mind that you just proved the negative thoughts irrational. Save that memory and use that to gain confidence