How to make watermelon mousse

This recipe was fairly straightforward, but there was not much whipped cream so it didn’t fold in, it was too liquify to fold. And the cream separated out of the mixture and floated at the top. I kept mixing it back in before I poured it into the ramekins, and that seemed to work, but it separated as it refrigerated and I ended up with a layer of cloudy jelly under a layer of pink watermelon. I did double the recipe, but I made extra sure I got all of the measurements right, so I’m not sure how that happened.