I've heard corn sugar is a bad idea because it acclimated the yeast to a simple sugar and may reduce attenuation in your beer.
At this point, leave it alone. Maybe check yeastcalc.com to see what kind of growth factor to expect from that starter. You may need a second step of a starter, but that will likely adjust your timing. You'll have to decide for yourself if you are under pitching and if it is worth it to move forward with your current starter.
Good luck and happy brewing.