ᐅ IKEA Besta Series Back Panel Lacks Stability?

Hello, maybe someone can help.
I bought an Ikea Besta cabinet
(60x40x128cm (24x16x50 inches)).
Assembly was easy, installed the doors and shelves. While adjusting the doors, I noticed the cabinet frame is warping to the left.
The frame is aligned straight and not mounted to the wall. The doors are on the right side. I have to push the top of the frame slightly to the right because it pulls to the left, about 2.5cm (1 inch) I would say. In my opinion, the back panel is causing this since it doesn’t provide the necessary stability. This becomes clear when you remove the top panel. The side panels are warped to the left. Does anyone have any ideas without mounting the cabinet to the wall?

There are two options:
1. Remove the back panel, align everything at right angles, and then reattach the back panel accordingly.
2. If it still seems wobbly, you can stabilize the piece of furniture by attaching a diagonal strap while it is properly aligned.

wiltshire schrieb:

There are two options:
1. Remove the back panel, align everything at right angles, and then put the back panel back on accordingly.
2. If it still seems wobbly, you can stabilize the piece of furniture by attaching a diagonal strap while it is aligned.

The thing is: the back panel is not fixed but only inserted into grooves. I already had the back panel removed – it didn’t help.

Then the solution with the strip applies—provided the shelving unit can be forced into position with the back panel installed.

wiltshire schrieb:

Then the solution with the strip applies—provided the shelf can be forced into position with the back panel installed.

What type of strip would you use?

Anni__Ra schrieb:

The thing is: the back panel is not fixed but only inserted into grooves. I already took the back panel out – it didn’t help.

Weren’t there any nails included to nail the back panel to the sides?
If the back panel remains movable in the grooves, it will never be stable.