I lied on my resume and got an offer … conditional on completion of background check. How screwed am I?

Hi all!

So, exactly what it says. I lied on my resume, and recieved a conditional job offer contingent on the completion of a background check and drug screening from a publicly traded company. I was truthful about where I worked, but inflated my tenure at several positions in order to conceal a break.

They already asked me to provide contact information for each job earlier in the process (I put the cell phone numbers of two close friends who agreed to be in on it), before I got the job, and haven’t mentioned it since.

I was notified that the background check usually takes 5-10 days to complete. I’ve been in a similar situation before and retained the offer, but know that every company’s processes/contracting background check company are different.

How worried should I be? Does anybody here have a similar experience?

Edit: Each discrepancy is 6-7 months. There are a few roles that I was 100% accurate re: dates for. Mainly because I have professional references for each.