Your upper should have a barrel nut. Regardless if there is a freefloat handgusrd or not. All barrels are 'free floating', handguards can freefloat, clamp, or screw into upper and/or barrel.
Discussion
I'm probably using incorrect terms.
I know the barrel nut is installed, and the rail is over top of it. The base of the rail where it meets the upper has a section where two hex screws secure it.
But I got the handguard/rail dirt cheap and idk if it's intended to tighten until the metals wings clamp together, or if there is a missing piece that is supposed to go between them, like a washer or something else to provide tension.
Gotcha. I would think not, but every manufacturer is different.
Try to crank down a bit and check it
Many don't. Some have a spacer. If it's cheap, likely not. There should have been a torque spec to hit. If not, we can infer a torque spec from the size of the bolts.