Watermelons???

Ok, I know I've been really happy about my cucumber plants growing and making fruit and all but I have some really bad news. I don't have any cucumbers. Apparently they're watermelons instead. I thought I planted cucumber but due to the lazyness inherent in the way I garden, they either didn't come up and I planted more than one thing or I somehow mistook watermelon seeds for cucumber seeds. They look nothing alike.
I could still be mistaken even since I have never grown watermelon from seed before. They could be some other melon entirely. They are still little green balls after all and who knows what color they may turn.