The remesh feature is affecting my whole shark even when I have preserve face mask on, and it makes it all look pixelated and blocky and I cant smooth the fin without making it disappear
The preserve face mask option only preserves the mask you paint, NOT the geometry that is masked. As far as I know remeshing cannot be isolated to certain parts of the mesh - it's always a global operation. This is one reason I prefer dyntopo most of the time.