Simple, you came up 3" short...
My thoughts and not to question your bending skills. Common bending problems:
*offsets are measured center to center of left to left, top to top, or bottom to bottom. Back to back 90's are measured outside to outside
*back to back bends requires the bender or pipe to be rotated 180 degrees for the second bend
*the tape measure got the better of the one who's doing the bending and measure wrong
The two bends in a back to back are bent from two different marks on the bender
