this is one of those perfect examples of how an error can add up-
with that many pieces across it is easy to wind up off---
if you are only 1/8" off on a seam you may think---that's not a big deal- i will leave it---but in 8 seams you are a whole inch off!
one of the reasons it is helpful to trim/square up & check for accuracy as you go-
it could be all of your pieces are correct- but your seams somewhere along the way started getting a little larger- or smaller---so, you should look at the back & see where you started having the problem & go back that far- hopefully it's not too far back...good luck-
people often will think---only 1/8" or even 1/16" of an inch is nothing to worry about---but if there are many pieces---those variations to add up---quickly