Iron all the way around the bottom edge, removing your pins as you go. Repeat with the other leg. If you are worried about making mistakes, this would be another good time to try the pants on again and take a second look in the mirror. The hem can always be re-measured and ironed again before you sew. Replace your pins to hold everything steady while you sew.
Once you have ironed your hem in place, you’re ready to sew.