make sure you take it back to the people and make them aware of the problem. i'm sure they will work something out for you. try to get your car checked out (by another place) and get them to pay for it.
my friend took his car to jiffy lube once, and the guy ended up cracking his radiator b/c he leaned on it. he brought it back the next day, and they said they werent responsable.
good luck man... sorry to hear that. Nothing should be really wrong but a REALLY dirty engine bay. that is, if you still have a decent amount of oil left....