#1 - Yes Chevy's ordering system is extemely outdated and not customer friendly, particularly when it comes to pre-orders like this. It's something many manufacturers struggle with, one of these days they'll get caught up to the 21st century (I predict 2105 but I'm an optimist
).
#2 - To the OP, your frustration is somewhat understandable and your dealer did mess up if they promised a May delivery. Either way I don't really care if you're buying a Camaro, a Kia or a Ferrari there's really no reason act quite so fruity over any pre-order car.