Swampass is onto something. If you took gravity readings with your refractometer before fermentation and then also used your refractometer to take gravity readings after fermentation, the presence of alcohol in the finished beer will throw your numbers off.
I'm taking a stab here based on converting your OG and FG back into brix. If your OG was 1.052 that works out to about 12.86 brix. And assuming you took your FG using your refractometer, then an FG of 1.028 will have read about 7.06 brix.
I'm using Sean Terrill's refractometer FG calculator. Here's his website if your interested:
Anyway, with an OG of 12.86 brix and an FG of 7.06 brix according to Sean's calculator, the actual gravity of your final beer is 1.0139 which is right around what you were looking for. So...good news...your beer is doing exactly what it's supposed to be doing.
P.S. there is a Basic Brewing Radio podcast with Sean where he talks about using a refractometer and the research he's been doing. Great stuff. You should check it out. It's available free in iTunes.