I transplanted a bunch of plants and I was sure I labeled the plastic cups with marker but either it washed off or I forgot these ones because I have 3 plants I can't identify. Here is a picture of one with a cucumber plant next to it.

I planted cucumbers, peppers, cantaloupes and watermelons. I think it might be a watermelon but I'm not sure. Can anyone help identify it? Thanks for any replies!!