Does my Kimchi need to ferment longer?
You can eat kimchi at any point.  More fermentation/time simply means more funk.  It is more likely that things are floating, your only risk is mold forming on the surface.  You can add a weight of some sort to keep the exposed ingredients under the liquid, but if you are going to keep them sealed like that, mold formation is less likely, unless you remove kimchi with fingers or non-sanitary utensils.  You can also add brine, but I don't think that is as common in a kinchi situation, as it is in other pickling situations.