Too Short, Too Thin

I have owned a lot of rash guards over the years, for surfing, so I know what a rash guard should be. I think this feels way thinner than any I've ever bought. Worse, it is too short. I'm just over 6' tall and thin, I bought an x-large like I always do. It is just fine as far as tightness goes but it leaves bare skin between the top of the trunks and the bottom of the shirt. If I raise my arms it rides up to my navel and the bare gap jumps to 4 inches. It should have been made easily 4 inches longer at the waist. I don't know if a larger shirt would be longer, but it would certainly be too baggy. I have to return it.