People do not fly backwards when hit by a shotgun blast. If this shotgun were powerful enough to do that, then the person firing it would be blown backwards with equal force.
When Wendy receives the phone call, she says that she can be in Paducah (Kentucky) "in a couple of hours." Actually, Paducah is almost six hours from the Lake of the Ozarks area.
Wendy visits the Lazy-O and used a key card to enter Jonah's room. She places the card on the desk and attempts to a the computer. As Wendy leaves and speaks with Sam she does not return the key card. However, she clearly feels no obligation to Sam and doesn't care if he has to retrieve the key card himself.
About 20 minutes in as Marty gets out of his car, you can see camera brackets visible in the corner of the car driver door window. As he walks by, you can also see the one in the passenger window through the windshield.
Ruth suggests to Wyatt that they escape the Ozarks by getting a boat and going up the Missouri (River). Although the Missouri River IS accessible from the Lake of the Ozarks via its primary inlet, the Osage River, the direction and navigation would require them to go quite out of their way east before reversing to go back west and then northwest up the Missouri River. It would make much more logical sense to simply hop in any of their available cars and drive away.