Fake it. Fake all of it. Imagine how OftenBen+ would handle such a situation. Imagine what a person who is comfortable in such a situation looks like, try to emulate that as much as possible. All of which would be easier if I didn't sweat like a whore in church at the slightest stress, but it's the best I've got.
I do something similar to this because I'm afraid to not live a full life due to a fear of failure. I make very impulsive decisions like moving across the country and then doing it again even though I didn't think either of them through. They ended up being some of the shittiest most worthwhile times in my life so now it's easier to convince myself to do things. Just have to fake it until it gets easier.
I feel that this is the best answer. It's not so much lying to yourself, more like making a game out of it, say pretending you actually are that confident person doing that confidence-requiring thing. Humor is an incredible tool. Easily mistakable for confidence :-)