What type of bath panel? Flat surface like one made from sprayed MDF - in which case velcro and wooden vertical hidden support fixed to the wall
or if vacuum moulded plastic then usually there's a lip that goes underneath the top rim of the bath and I fix a batten to the floor at the bottom. If the height of the bath is higher then the panel then you'll need to make up a piece of timber - cross section like a thick L ...the vertical stops the panel falling backwards and the thickness of the bottom piece gives you the extra height. 'swot I did.
If the bath is standalone or one end is standalone then I think that you have top get special corner pieces from a bathroom supplier.