Hi Brenda, this will work for your fiberglass tub
Try a mixture of blue Dawn and baking soda. Make a paste of it and rub with a SLIGHTLY damp sponge. I'm not sure, but it might just work. Baking soda is a very gentle abrasive that won't scratch and will even clean gunk off of pot bottoms.
I gently scrub clean mine with Comet then completely towel dry the area. Then, w/a separate dry cloth, apply The Original Gel Gloss product. Rub it in good and buff it dry to a super glossy shine! It will look brand new and the Gel Gloss helps keep your tub & shower cleaner longer!
We bought an abandoned home that sat empty for 6 years. The tub and showers were nasty. I used Magic Eraser for bathrooms and it worked really well.