Luca, I have mentioned this a few times on the forum - there are so many threads on cases that it is impossible to keep up - stitch a seam 1cm in from the long edge, trim off the surplus, and the N800 fits snugly in the soft case without falling out. i.e. turn the case inside out in order to stich and trim.

The new PSP Slim cases might be a better fit, they should be out soon.