Whatever pattern you are trying to follow is off a bit.
If the center bar is supposed to be a bit wider, the the two edge bars must be smaller. Start with the center--if you cut it 3" wide, it will be 2 1/2 wide after seaming. That will leave you needing two side bars at the TOTAL finished width of 3 1/2" OR 1 3/4" each. So add a 1/4 all around and you'll now have two edge pieces cut at 2 1/4 in before seaming.
Still 6 1/2 long each for a finished block of 6"