All indications are the melon is ripe; however, when it is cut open, it is ripe around the seeds but the part around the rind and the center is white. What would the problem be?
Is My Watermelon Ripe
Certified GKH Gardening Expert
The flavor will be the real determinator on this, but it does sound like it was picked a pit early. Make sure that when you pick it, it feels heavy for its size. This article should help as well: https://www.gardeningknowhow.com/edible/fruits/watermelon/pick-a-watermelon.htm