Exaggerated how long I worked somewhere but did truly work there

Hello, I recently got a new job and passed the interview and they sent me a background check, On my resume I submitted I extended the times I worked at some jobs but I did actually work at each of them. I dont have any criminal history or anything along those lines, and on the background check they have a spot for me to put exact dates and whatnot, and it's through Cisive that the background check is taking place. I feel like its best if I reach out to all companies HRs and ask how long I really worked there, then revise my resume in case they ask me about it. I would put the real dates on the background check though. Any advice is appreciated especially when it comes to finding out how long I really was with these companies.