A fender washer is a big washer with a small hole, right?

I can't actually bend those with just my hands; I guess I'm pretty weak.

I wonder if the screws I used in the rest of the build are likely to be a problem too -- the rest of the frame is all 2x4s glued and screwed together. The forces there are somewhat different, though.

I'll be putting less weight on it after I fix it too; I was foolish thinking that the bookcase was reasonable.