I've done the same thing, your steerer will be fine. As mentioned, a bit of nail polish resin should protect that area. When I cut my steerer now, I just leave the fork in the frame and use a few throw away stem spacers to level out the cut. I then use a flat sander to smooth it out. Afterwards I just use a leaf blower to remove the carbon dust and wipe everything down with a wet cloth. Since switching to this method, I've always had a perfect cut.