Well, it's some sort of a squash. "Pumpkin" is a somewhat ambiguous term, as all pumpkins are squash, but not all squash are considered to be pumpkins. Since it's round, it might still be considered a pumpkin. Time will tell. From what I can make out in the picture, it's probably from the c. maxima family. Some of these get pretty big. Most have large, fat seeds.

George
Tahlequah, OK

Could it possibly be a honeydew melon?

I think its a pumpkin...I have one that looks just like that now and I have no other types of plants with my pumpkins.

Are we seeing a white bloom? It looks like a pumpkin, or squash, but if the bloom is white, it could be a gourd.

Jan