I'm a sinker

[BKKGuy]

I have started the TI drills for freestyle and am up to the Shark Fin. However, when I bring my arm up to the Shark Fin position, my upper body sinks to the point where just my elbow is above water. When I see videos of other swimmers doing the Shark Fin they sink just a little bit.

Is this a problem? Is there somthing I can do about it? Will it interfere with arm entry when I get to that point?