To me, based most particularly on the view from above him, he looks just about exactly right.
He looks good. See how his belly is tucked in? He also has a waist. So he’s good. Kitten will go through chubby stages. One of my kittens gets fat right before she hits a growth spurt. Then she leans bout again. I was really worried about food in the beginning but kittens eat a lot and they are growing very fast.
This is hopeful -Keep an eye on him, but I believe you can relax.