Yes that is right. Measure the template from the center to the point. That plus 1/2" is the width you need for each strip.
So a 4" HST = 2 -3 1/2" wide strips by as long as you want.
Sew strips together open and iron the seams.
Set the 4" template on the seam on point. Two opposite corners need to be on the seam. Rotary cut accurately around the template.
You will get a 4" HST. Pay attention to cutting accurately and you won't have to trim anything. Don't let the template move while you are cutting.
I use sandpaper strips glued on the back of my template to get a good grip so it doesn't move.