Close gap between bathtub border and wall
It's a bit hard issue to handle, because, as @isherwood indicated, that tub's destiny has been changed.
I can think of two groups of 'fixes' depending on how much You are motivated:
a. change of usage - bathing while standing must go, fix the shower head lower, try to use it kneeling or so, check if sutiation changes, consider using the tub as a bath tub
b. change of environment - consider changing the cloth, but this time let it start under the showerhead to let water be gathered by it before it reaches places You want to avoid getting wet; this must include change of cloth's suspension