Will I snap my derailleur? (too large front chainwheel)
As suggested in the comment above, I would take it back and ask them to add a few more links. It's totally negligent of your LBS to fit a chain that cannot accommodate every combination of gears, however silly. There's always a chance you can fumble a shift and end up locking the drivetrain, as you've already experienced. This is definitely dangerous - if the pedals suddenly lock up and surprise you, you could crash. Another possibility is that if you keep pedalling, the rear mech will be pulled into the spokes, trashing both mech and wheel.

There is also an outside chance that with the new, larger chainring, you have exceeded the take-up capacity of the derailleur - meaning that adding links will result in a slightly slack chain in certain other combinations of gears. This is less of a problem, but bear in mind your chain may jump off if you run the small ring with a small sprocket on a bumpy road.