The shop said YOUR draw length was 31.5 inches, or the bow was set to that length. There is a difference. If you are shooting your dad's bow chances are it doesn't fit you. Compound bows are fairly individual things in how they fit the archer.

If you want to try some sights go get yourself some cheap 3 pin fiber optics and slap them on your bow. Then sight it in. Just anchor the same way you did and set the pins at the distances you want them. Most use 20,30, and 40. I wouldn't bother with a peep if you have been shooting instinctively and do pretty well. I doubt you will need one unless you want to target shoot.

If it's possible post of pic of you drawing your bow and someone will let you you know if your bow is way to long or not.

Paul