shadesofjay, thanks for posting this. I just bought a box of clementines and have never finished a box in my life. This is a good use for them.
What Cathy2 said is right on. You can use a lot of things to preserve food, including salt, sugar, alcohol, and vinegar. Curing generally implies salt. Jams, jellies, conserved, and preserves generally use sugar (as you are in this recipe).
If part of the fruit remains above the liquid, you risk that it will begin to rot. If you can't keep the fruit submerged, I would recommend trying these ideas: first, try to find a smaller vessel so that you can pack everything in there. Second, as Cathy said, try to find something that can push the fruit down. Third, if all else fails, mix the fruit every couple of days so the same little bit isn't above the liquid.