Tub installation/level questions
The ledgers are not meant to carry any weight. All weight should be supported by the base of the tub. The only weight that the edges of the tub should carry would be the weight of the wall panels which will be reduced as the top edge will be screwed to the studs.

If it was me, I would first remove the screws and gently pry up on side of the tub to see if the plastic separation will allow the tub to lift freely. If I felt too much resistance, I would leave it be, reinstall the screws, and continue with the wall panel install.