Those warning stickers are to protect the manufacturer from product liability lawsuits. Quick release wheels are, as you suspect, hard to screw up...especially if the technique was demonstrated to you by a bike shop employee.

I'm not sure what kind of brakes you have or how they were affected by your fall. The bike shop will tell.

As for the frame, banging it repeatedly with a trunk lid can't be good for it. Inspect the frame. Are there dents? Structural damage is bad. Have the bike shop check that out, too. Is the paint chipped? A little touch-up paint can fix that.

I'm thinking that you probably haven't done any real damage to the bike, but let the mechanic check it out.

We all have bad days. We all fall for no apparent reason, too. Well, I fall for no apparent reason. Wear your helmet. Keep riding. Cheer up! All will be well.

By the way, were you hurt?