If you answered that question incorrectly and said no one can claim you, when your parents try to e-file their return that claims you---their return will be rejected. They will not be able to e-file their 2019 return at all. They will have to print, sign and mail their return, and you will end up having to file an amended return for yourself.
Your return will be rejected if your parents claimed you and you didn’t submit that fact on your return. If you have filed and they file after you then their return will be rejected. No one will go to jail.
There are 2 scenarios.
1. The parent could but chose not to claim the dependency. When the child answers someone else CAN claim me that would be true. This can be a choice when the parent wants to allow the child to claim the education credit, for example.
2. The parent could not legally claim the child as a dependent. If the child erroneously says that someone else can claim them, the child loses the opportunity to receive many tax credits.