TI Experts - Help Needed

I recently started the Perpetual Motion Freestyle in 10 Lessons program.  I completed lesson 1 and seemed to do well at those drills (superman glide, superman flutter, laser lead flutter).  In lesson 2, in performing laser lead rotation I noticed that after I rotate, I have a difficult time staying near the surface of the water.  As soon as I rotate, I begin to slowly drift toward the bottom of the pool.  It is even more pronounced in skate position where by the time I run out of breath, my hand is basically touching the bottom of a 4 foot deep pool.  I seem to stay horizontally level as I'm sinking (i.e., my legs are not sinking any faster than my upper body). 

My question is - is this normal r is it possible I'm doing something wrong?   Any ideas on what I may be doing incorrectly?  Also, do you recommend just continuing on to lesson 3 and hoping it works itself out or should I continue working on lesson 2 (or lesson 1) and try to figure out what I'm doing wrong.   

I don't think I'm stacking my shoulders.  My guesses are it is either not relaxing enough or that I'm sinking because I'm exhaling air.    Thoughts?