Can I back out of Invisalign once the aligners are made and I've only paid for them to take impressions?

I want to back out of Invisalign even though the aligners have been made. I haven't gone in for anything other than the impressions. I don't want to be charged the $1500 I was originally quoted and want to cancel treatment. I already paid $100 upfront and don't expect to get that back. Do you think my dentist will try to charge me for the aligners even though I haven't worn them and don't plan to? I'm really worried about this. Can I really be charged for something that I haven't started to use?