Did something wrong, help please

DanP said:

Still new at working on my bikes.

Dealing with my Cervelo P3, D/A 10 (TT bike, non-STI lever shifters on bar ends)

Had to replace a questionable rear tire - first time dealing with the rear. So set the gears to 39/12 and removed the wheel.

When I had the wheel ready I mounted it setting the chain back to the 12t cog.

But when I spin the pedals with a couple of revolutions the chain goes out in the rear (to the outside of the 12t cog). Attempting to shift to a larger cog works but it fails to go on the largest cog (25t).

Almost as if I went off by 1 cog somehow.

What is the best way for me to recover? I'd rather not start playing with the rear derailer as I could mess things up worse - and I have a race this weekend and definitely need my 53/12.

Hoping there is something really simple that I missed here.

Thanks in advance!

Axel seated in the dropouts correctly?? Derailer limit screws are not self unadjusting.

Thanks, I just double-checked, it is seated correctly.

Only thing I can think of is that the partial weight of the bike resting on the RD messed it up? I was real gentle and I doubt this thing is so frail.

Figured it out, someone knocked the bike while I had the wheel off and now its adjusted and back to normal.