I believe you will end up with a longer quilt. After you sew the strips together the next step will be cutting the specified width of each Bargello strip so the only thing you have changed is the length of each Bargello strip. If you had say for example 10 colours to sew together your strata which in your case is the 2 1/2 " strips sewn together, would measure 20 1/2" by width of fabric and the original pattern using 2" strips the strata would be 15 1/2" by width of fabric. Therefore your overall design will be elongated. If your making a lap quilt that is say 60 " long your quilt is now going to be approximately an additional 20" longer.