After looking at the pattern -
I'm making a couple of assumptions:
1) You are using a jelly roll
2) The strips are 2-1/2 inches wide
If you read all through her directions - it says you will need to trim the strip ends to line it up - after you put each section together - (I do not find that reassuring!)
Rather than try to square the blocks up - I would just cut 1/8 inch off each of the 2-1/2 x 3 inch pieces (then they will be 2-1/2 x 2-7/8- then you will end up with a unit that is approximately 7-1/4 wide by 7-1/2 high
Then you won't need to fight with the strips - assemble it in the way that is illustrated