I got the PST this weekend but I am not sure about it...does it look too small on me?

I think it fits your proportions nicely so if it hold all your belongings without being overstuffed then it's a keeper! Only consider the GST if you need more room.
 
I love the look and the size of the PST on you! I would definitely keep it. I definitely prefer the look, size and comfort level of this bag to the Medallion Tote.

-Stephanie (pond23)
 
It's definitely a keeper. The proportion of the bag suits you perfectly.

I completely understand where you're coming from though. I have lots of massive bags, so anytime I downsize I always feel like it looks like a pimple on a pumpkin! But seeing the PST on you has made me want one!