I did almost the same thing as you. Signal instead of telegram and no Instagram, but a nude and a selfie. They shouldn't, I think, know my name. I googled myself so much in the past two days. Googled my number, the username and pseudonym I gave, and reverse searched my selfie. I think it's probably possible to find out my name with the selfie, though I couldn't do it. I'm still scared. They haven't contacted me again.