I'm not getting it. You say that you have 1/4- inch seams.Okay. You say that you noticed that some pieces are 7/8ths inch wide. Okay. You say the srtips are supposed to be 17 inches wide, and most of yours are in the 18 inch range. Okay.
I'm not getting gow this is an issue. Can't you just cut the 18 inches down to the 17 inches? Are the pieces supposed to be larger or smaller than 7/8ths? are you supposed to have specific shapes once the strips are sewn together?
This is not enough information to be able to offer solutions or suggestions.
What pattern are you using? Can you show us what you mean, or what you need to change?