How to prevent nail polish from dents and scrapping off?

Try waiting a little longer between coats.

If you put on the bottom layer and then quickly put on another layer, the bottom layer might not dry so well, even though the top layer feels nice and dry. Then when the fingernail rubs up against something, the bottom coat might slide and take the dry coat off with it.

I don't use that brand often so I'm not as familiar with it but I know that with a lot of nail polishes sometimes when they feel dry to the touch they may not be completely hardened yet. So maybe you could try giving them a bit longer to dry. If that doesn't work it always could just be a bad nail polish, I've used certain brands before where I felt like they were never fully dry and they were kinda movable on my nail like how you said you got dents when you grazed something hard. I hope this helps!

I do like China Glaze polishes, but each individual polish is different regardless of brand. A 99 cent polish could be a thousand times better all around compared to a $14 polish. Nail polish is odd like that.

Anyway, I highly suggest purchasing a fast dry top coat, particularly one called Seche Vite. It will change your life. Haha! But seriously, it's amazing. You start with your base coat, then polish your nails as usual, but don't let the layers dry in between. Just paint one hand, paint the other, and immediately go and do a second coat on your first hand. Once you've put on as many coats as you need to make the polish opaque, put on Seche Vite. Put it on top of the wet polish. Seche Vite dries all layers of polish down to the base coat. Within 1-2 minutes, they're dry to the touch. Within 15 minutes, they're essentially undentable. It's an amazing product, seriously.

If you don't want to buy Seche Vite, I suggest doing thinner coats and waiting about 30 minutes in between each. Make sure the environment is not moist (so don't do it in your bathroom or after a shower). Make sure your nails are completely dry (don't soak them or shower immediately before). Make sure it's not particularly hot.

You can apply clear nail polish ontop of your nails to possibly protect it better.