Sometimes it looks too small to me, too. You also look like you're a bit forward on the saddle (although I don't know how I look on mine..), and -- maybe it's the sweats -- it looks like your shoulders are hunched a bit and your elbows turned way out.

Starting with a super-low saddle has really thrown me off, I have to say.

Keep riding as it is for now, and put some more time on the bike -- some things you won't really feel until after an hour or so (but if you never ride that long at a stretch, it won't matter so much anyway). And, assuming they'll let you, go back to your shop and try the next size just to be sure.