A small peony, herbaceous, can not be cut back to make it fuller. A tree peony can be pruned/cut back to make it bushier or taller depending on the cultivar. You probably have a herbaceous.You can help it by keeping the grass from around it and giving a very light feeding of a vegetable fertilizer now and in September. I use 10-10-10 myself but others use different types. You can use the pelletized fertilizer but in some soils the pellets remain and do not dissolve so that the soil lots like it has lots of snail eggs.

A good book for a beginner is Pamela McGeorge's "Peonies". Your library may have a copy of they could get it for you using the lending system many libraries have. Try not to cut the plant down. 1. You might find the foliage very interesting. 2. Foliage feeds the roots. An older plant can stand the foliage being removed better than a younger plant. This fall, early winter carefully remove the foliage after it has browned by cutting the stems,I am assuming it is herbaceous not tree, about three inches above the ground.

Since you are in Oklahoma and probably are in the heavy rain area this year when it becomes dry you can put about a inch of mulch arround the plant to hold the moisture in the soil arround the roots. If the plants starts wilting in the 100+ temps you sometimes get do not water it during the day. A little shade cloth can help the wilting but water at 100+ may cause the plant to cook.

When it finally blooms please post a picture.