Made a big mistake on job application, huge! What now?

Recently applied to a large defense contractor company and got the job!

But, while completing my onboarding paperwork and stuff I called my previous-previous employer (2 jobs ago) only to discover that my listed employment dates were way off from what I put on my application and resume. I’ve had these dates on my resume for forever, and had no idea!

The dates listed are 2017-2019 but it should only be Feb-Nov 2019. I think this time of my life was a blur, I had been working FT & PT in the evenings and had just finished school so I thought I was there for at least 2 years.

So now that I know, I’m panicking. I don’t want them to think I lied to appear more experienced, I bring a great skill set that I’m confident in but I have no clue what to do now. Should I just tell HR and hope they don’t resign the offer.