Could you please post a link to the actual pattern? Often there is some other factor involved and it will not be apparent if we are given only parts of the pattern.
1 1/2 inches times four strips will equal an unfinished panel that should be 4 1/2 inches wide.
Try a sample to make sure that your 1/4 inch foot is accurate on your machine. Take two scraps with a specific measurement. Now sew them together with your 1/4 inch foot. Press and measure again. The measurement should be 1/2 inch less than the combined total of the width of the two scraps.
I have one machine that has a 'problem'. I actually did not notice it until I made some blocks for the same quilt on it and on another machine. My 'problem' machine does not have an accurate 1/4 inch and it took a bit of trial and error until I figured out what change I had to make on the needle location (left/right) to achieve that perfect seam width.
Last edited by GingerK; 02-27-2019 at 06:30 PM.
Reason: more info