Hey there! There are a few solutions. The easiest is probably to take the Leveller tool, set the Blend Mode to Divide, then set the Value to 1.018 - that should squash everything down so that everything at 0.509 becomes 0.5. Either that, or you can just adjust your gradient so that the ocean colours start slightly higher. If you're using water maps, you could also simply fill your water table slightly higher so the water appears in the right place.