Returning player account confusion

I am sure this has been asked a lot, but nothing I have tried has worked. I played Runescape a long time ago, I would say easily 10+ years ago. I logged in again maybe 6 years ago just for a weekend. I recently wanted to play again. I tried logging in and it told me to upgrade my account to a Jagex account, which I did. I downloaded the Jagex launcher and imported my character. I selected OSRS and clicked play. It sent me all the way to tutorial island after logging in. I know my character was around combat level 70. I then chose Runescape, which im assuming is RS3, and it logged me in as a level 75 character which seemed more like my real character. If I want to play OSRS do I have to start over? or is there a way to make that account back into my OSRS character instead.