Generally speaking, yes. It is unprofessional and can make it seem like you don't have your head on strait. If this is your first experience with the gallery a bad impression would be made and could hurt your chances of being asked to participate in any future shows or exhibitions. As an artist signing with a gallery you have an obligation to honor whatever contract you signed, this includes the entry and the price you assigned it. If it sells consider it a lesson for next time- if it doesn't no harm no foul.