My RL first name is sufficiently common that I can relate! (More technically, my legal first name is the common “short”, so people assume it’s the long version, an assumption that is true 85% of the time, but I’m in that 15% minority where it’s wrong. And that 15% includes it being a short version for other common names too.)
I’ve got a total of two pen names, the one here, and “Dragon Voldemort” for my Harry Potter fanfics. (I made the DV one first, but once I started writing originals, it no longer fit). Yep, I’m on FF.net and AO3 with the DV penname.