GDPR cannot destroy your business, because GDPR penalties have to be proportionate.
You mention forgeting to file some paperwork: here's an example of an organisation handling sensitive medical data who, by law, have to register with the regulator. They didn't register.
https://www.bloomberg.com/news/articles/2018-04-26/u-k-healt...
> The U.K.’s Data Protection Act requires all organizations processing personal information to register with the U.K. data regulator. Although handling sensitive data on recent patients and those needing regular health care, Cera also failed to register with the Information Commissioner’s Office until February this year. The ICO said in a statement that it would only consider “enforcement action” if a company failed to register despite ICO advice.
They didn't even get a fine. (Maximum available fine at the time: £500,000.)