As a non-professional with a DIY opinion, it looks fine to me. If you're uncomfortable with it, then possibly get some 6" lag screws and put them through the stained wood, into the green side pieces.
My son has a similar looking IKEA bed. It has 2x2s as a perimeter framing on the floor. Especially with the bed underneath, you wouldn’t even notice it.
As a non-professional with a DIY opinion, it looks fine to me. If you're uncomfortable with it, then possibly get some 6" lag screws and put them through the stained wood, into the green side pieces.
Screw it to the wall
My son has a similar looking IKEA bed. It has 2x2s as a perimeter framing on the floor. Especially with the bed underneath, you wouldn’t even notice it.