can I go back to my dentist and ask him to redo the crown without having to pay again?
If you are unhappy you certainly should approach the dentist with your concerns and ask his opinion on the match and what he is willing to do as far as a remake. Most dentists do not want unhappy patients walking around. Maybe it is a difficult case where he feels this is the best that can possibly be done. I assume you approved it before it was placed either verbally or in writing? In any event discuss the situation with your dentist and hopefully you can get it resolved.