Did it feel like the brakes were applied? The Hill Start Assist will engage full brakes if it believes you're on an incline so that you don't accidentally roll downhill forwards or backwards. If the brake wasn't what was stopping you, it may have been the gears not engaging, in which case you may have a shifter problem. Definitely call the dealer; if it's the shifter, one day it may just not shift out of Park.
If you see three lines where you normally see the gear indicator, call the 800-SMART-USA for service; they may be able to help you over the phone. There's a transmission teach-in process, and opinions differ here on how it's done... the manual states that if it fails once, don't try again. To be safe, call the official support line.
If it is just the hill start assist and the car's new <500 miles, it will get softer with time... it starts out really aggressive. Maybe because they planned for parts to wear down over time.