They must be sanded off. I got this hasp drill bit that works wonders. Grind away for while and it it will become completely flat. Safety tip - wear glasses as shards of plastic fly everywhere. Marital bliss tip - do it outside as shards of plastic fly everywhere.
Metal hinges can be obtained on eBay or use The Google. Much sturdier than the plastic ones. Line them up, drill holes in the acrylic and attach. (That crack was there before)