I didn't tin my solder bit...now what?
It depends on whether the untinned tip coating is just covered with a layer of crud, like flux residue, or is now all oxidized.  If the former, you can probably carefully clean it off (with the iron cold, of course), then power it up and tin it properly.  If the latter, this is a unrecoverable error and the part of the tip you didn't tin is now useless.