2nd degree burn, I got one on my arm about that size when boiling popcorn grease splashed on it.
You have to pop it, get a safety pin, be sure to sterilize it first, and just stick that needle right in. I only made a small hole and squeezed out all the liquid inside but you can do whatever you want, then just peel the skin off and your good.
It won't hurt, that skin is dead, the new skin under it will be tender so wear a band-aid.
Also, prepare for a scare, I still have a birth mark-esque scar on my arm from mine.