Can I use enamel or acrylic to cover a VERY small chip in my bath tub paint?

They make a special paint for tubs and sinks to repair chips. It isn't expensive and you can get it at any big box store or your local hardware store.Can I use enamel or acrylic to cover a VERY small chip in my bath tub paint?
Neither will give you durability or long term performance in a wet environment like a bathroom. You don't say what the tub is made of but no matter the composition, fiberglass, enamel over cast iron, or acrylic, each has its own paint manufactured specifically for touch ups on those surfaces. You really need to know what the tub is made of and then head to the home improvement center to purchase the correct touch up paint for it.