Well, your tank got scratched because of an understandable error.
You shouldn't have had a magnet cleaner in the first place on it.
Lessons in life are usually learned the hard way, and that includes the damn expensive ones.
Is it not possible to turn the tank around, leaving the scratch on the back? If it's scratched all the hell over, then you're stuck trying to get rid of it. Some doofus will want to buy it for some use anyway - maybe for breeding guppies or something, who knows?
In the meantime, I would get acrylic again, only THIS time, make damn sure that you are the only one to clean the tank using your BARE HANDS ONLY...and watch out for reef critters that could make this a dangerous prospect. I see green tint in 75s and 90s at the store. That's why I would go with acrylic anyday. Never mind the bonus of lighter and not leaking.