It looks like a watermelon plant from what I can tell

The leaves don't seem to resemble any watermelon I've seen. But this plant is most likely a cucurbit and therefore related.

After looking around a little more online it could actually be a pumpkin plant but being that small it's hard to tell. I've seen watermelons with foliage that looked like your pic and then I've seen watermelons with the alternative foliage that you see if you do a search on Google. Looking through different pics of pumpkins though - it seems there isn't much variation in leaf shape. Did this plant flower at all this year?

Here is a link that might be useful: Pumpkin Pictures

It looks like a European cantaloupe (Cucumis melo var. cantalupensis). They are similar to North American ones but don't have the netted skin. They also have orange flesh.

Forgot to add, they are also called Charentais melons.

Here is a link that might be useful: Pics

Thanks everyone for your help! This plant has only been growing for about a month. And yes, it did flower and is still flowering. It just started growing in my community garden plot without me planting it. I'll keep you posted.

I wish it was a Charentais melon, only thing working against that theory is that these are not round, they're football shaped.