Yes get it switched back ASAP. Retro grading the oil could have consequences but as your not at high miles it shouldn't be an issue.
I've been running synthetics in my cars for about 20 years and all the warrantied oil changes have cost me the extra $$ to use synthetics every time. They are never part of the dealer's "free" changes. Dealers will usually charge you the difference in price between the regular and synthetics. If they try to stick you with the full cost you might want a word with the service manager. If you don't want to be taken to the cleaners by paying dealer price take your own with you. If you do, tell them you have it with you, where it is in the car and make them put it on the work order. Sometimes they will refund you the cost of the normal oil but not always, if they do stick with that dealer for future changes. They should never charge an extra fee for putting in the oil you brought with you, if they try it's service manager time or drive off.
Yes I have had them miss the 6 bottles in an open box on the passenger side floor and put normal oil in only to find out what an SoB I can be and make them do an immediate second oil change.
