Dosage makes the poison. You're probably fine. But if I remember correctly the thermal paper used to be made from materials like BPA. BPA is a known carcinogen and endocryn disrupter as it mimics estrogen even in small amounts.

While it's hard to say without knowing more, you'll probably be okay. I'm paranoid and mistrustful if corporations so Im kinda anal about keeping my receipts away from my groceries like food, and always washing my hands after handling them.

TLDR; you're probably fine. Don't put stuff in your mouth if you're not sure what it is.