Rear brakes

Hi and thank you for using 2carpros.com. It sounds like either a spring was not correctly installed or a retaining pin has failed. What I would recommend is to remove the rear drums and reinspect the components. Once your sure everything is together properly, then properly adjust them. These are the directions for adjustment direct from Alldata.

Using a suitable punch, knock out lanced area in backing plate or drum. If drum is installed on vehicle when this is done, remove drum and clean brake compartment of all metal. When adjustment is completed, a new hole cover must be installed in the backing plate.
Using suitable tool, turn brake adjusting screw to expand brake shoes at each wheel until wheel can just be turned by hand. Drag should be equal on all wheels.
Back off adjusting screw at each wheel 30 notches.
If shoe still drags slightly on drum, back off adjusting screw an additional one or two notches.
When adjusting screw has been backed off approximately 12 notches, brakes should be free of drag. Heavy drag at this point indicates tight parking brake cables.
Install adjusting hole cover in brake backing place.
Check parking brake for proper adjustment.

Additionally, here are general directions for brake replacement just to be sure they were done correctly.

https://www.2carpros.com/articles/how-to-replace-rear-brake-shoes-and-drums

I also uploaded a spring diagram to confirm that you have it back together correctly.

I hope this helps.
Cheers,
Joe