If the bath has lost its lustre and you want to get it shiny again use brasso, yes brasso , either the wadding or the cream and polish by hand , works a treat , if there are scratches use wet and dry paper ( wet ) at least 400 grade then 800 grade then polish with brasso but , importantly, do it all by hand as the acylic is only thin and you need to be careful.i have done a few baths like this over many years ( 1 was a £5,000 jacuzz ! bath) and all the customers were v happy . hope this helps.
Dave
p.s. if it doesnt work you need a new bath