Your frog is a perfectly healthy northern leopard. Ranids should appear a little plump.

Juvenile frogs are difficult to sex externally. Adult leopard frogs can be sexed by looking for the creases where the lateral vocal sacs are folded up; these will be just over the shoulders. They're not always easy to see, but if they are present, your animal is definitely a male. Male leopards will also develop thickened, callused thumbs and muscular forearms.