Thanks poppasketti, I’ve extended the starfield by duplicating and mirroring the frame on each side, then I removed the stars with the Dust & Scratches effect and I added new stars on a separate layer with the blend mode set to Screen, in order to hide the symmetry.
To get the rotation right, I’ve tried to cancel the existing rotation, so I could get the values for the angle and the anchor point, then I added a rotation in the opposite direction with a little bit of camera shake.