I shot a lot of prone starting at age 10 in the Cub Scouts, later as part of a competition rifle team and shortly after in the Army. GET COMFORTABLE! The idea is to be supported by the earth, not rigid. Get elbow bone contact with the ground, get your feet apart and ankles flat on the deck, and your right knee bent. Arrange your body at an angle to the target!
If you are working hard to hold this position, it's not right.
Get comfortable, get limber, get more practice - you will be fine.
(FWIW, I have been shooting rifle for 55 years and I'm NOT a fan of Cooper...)
I am another gun-carrying liberal veteran.