Using version on an iMac and can't get print image to print.

When i do the Print command, get a window with two images of the envelope. The one on the left is incorrect and the larger one to the right is correct. When I click Print, the printer, a Brothers MFC-7840, indicates that it is receiving data and then prints, but the envelope, which I have insert in the envelope slot emerges without any printing. I have been trying to figure this out for two years without success. So, I need help. Thank you.