Fear gets smaller after experience gives it accurate measurements.

Fear works from estimates, and its estimates are wildly conservative until reality corrects them. The first time you do the frightening thing, you learn its actual dimensions: how long it took, how bad it felt, what really happened afterwards. Those measurements are what shrink it, and they are unavailable in advance.

So treat the first attempt as data collection rather than performance. Do the thing, then afterwards write down what actually occurred versus what you expected. The gap will be instructive, and referring back to it makes the second attempt noticeably easier.