Originally Posted by Sneezy

Use it anyway.

Just make sure you tell the check-in agent you've already checked in online, but didn't have a printer.

You can even use OLCI to change your seat after you've checked when you're sitting in the RCC. You might get some strange looks from the RCC matrons when you go up and ask them to reporint your BP because you've changed your seat using OLCI, though.