Its hard for me to tell since I am not able to see you in person.
I would consider seeking another opinion of a doctor in town prior to the fix if you are concerned about this "fix."
But anytime there is a problem with the finish line, I would be concern for microleakage. The cement acts to seal the gap between the crown and the tooth but the smaller the gap, the better the success of the crown.
Oh, well in that case, you can wait til he cements it in and get a second opinion. But unfortunately they'll have to cut the crown off to remove it most likely. Another option is to ask him to temporary cement the crown for you while you get a second opinion on the matter. Its a delicate situation as you don't want to offend your doctor but at the same time, if you aren't completely comfortable with the situation, its probably better to check and make sure since it is your health, not his.
But if he already sent the crown back to the lab...I dont have the crown to get the second opinion.