I had this very same thing when I was a kid. It was the left side and had the same shape. It wasn't really a lump, but some type of growth.
A lump or rounder form would be scarier.
I saw several doctors for this cyst in my mouth. No one really had an answer, this was back in the 90's. Their only answer was to cut if off.
I refuse to go under a knife. It eventually went away. My diet was pretty bad back then. Lots of chips and fast food.
I made sure to clean my mouth more often when non alcohol mouth wash.
It eventually went away after a month or so. It would come and go.
It has been 7+ years and it hasn't returned. I did a lot of praying and was scared to death of this.
I think praying helped (mentally).