You did a good job on the armor. I never seen a stormtrooper this skinny. You may want to use foam as Scott suggested above, and use the heatgun to shape some of the parts to look smaller.
If you have more money, may I suggest upgrading the helmet to an AP or TE2 helmet? They tend to be one of the smaller accurate helmets (depending on how its constructed). You may also want to upgrade to an accurate sized chest as the FX one is soo big it tend to cover the ab buttons. You could also try trimming the chest a bit.
Assuming you have a holster, it looks like your ready for 501st application.