First thing you want to do is tidy up your piece of QG. You don't want any extra hanging out because it is a fusible and will gunk up your iron.
Take a sharp pair of scissors or snips, and snip the seam allowance, just down to the stitching line. If you snip the sewn line, no big deal, it will get covered up when we sew the horizontal rows. Remember, again, snip every other row.
1 1/2" ~ perfect. (And if yours isnt' perfect, ain't no big thing.)
Just snip and sew your horizontals and.....
Ta da! The finished block. Look at how pretty those points are!
Please let me know if you have any questions. I hope you'll give this a try!