Concerned of skin cancer

So, just for starters I know you guys aren’t doctors but you may know more than me. I also have an upcoming appointment in 1 week with my dr to talk about this. But I just want some opinions.

The other day I noticed this odd brown spot on my arm that’s never been there. I immediately thought it was chocolate. Once it didn’t come off, I got a little worried. Out of anxiety, I scratched it off and it peeled off. Now the spot went from red to dark red.

Does melanoma appear over night?

This is the best picture I have. It’s on my forearm. It doesn’t hurt. And it’s like puffed up.

Sorry, I’m an anxious mess and always seek reassurance.