Test with scrap fabric. Accurately cut three strip 1-1/2".
Sew with 1/4" seam, press and measure. Should measure 3".
If it's smaller make another test and use a smaller seam allowance.
If it's bigger make another test and use a bigger seam allowance.
Eventually you'll get it and the test will measure 3".
This is more important in quilts with more than one style block. If the quilt is made up of one block everything will match.