Your plant is a cantaloupe not a watermelon. They can both be hand pollinated. First you need female flowers. That can take a while. Try pollinating in the morning soon after the male flowers open. The best conditions are a warm night above 60F for low, some humidity, light winds, and sunny morning. Take a small brush and collect pollen from the males before touching the females. You need to get the brush way down into the flowers. Cantaloupe flower anatomy is more difficult than watermelon but pollination success may be higher. I only average about 20% success on hand pollinated watermelon.

Oh, sorry..

Ive planted watermelons and cantaloupe.

I got confused between them.

Thank you for you answer, It was very helpful! :)

Your plants are too small to start holding fruit. Give them time to get some more vegetative growth. I've got 'Ambrosia' vines right now that are 3' to 4' long and no fruit set yet. Near as I can tell; the more foliage. the better the melon.