Did you add the DME as well as the corn sugar, or did you forget the DME and *only* add the corn sugar?
If you added the sugar in addition to the DME, it will increase your gravity by about 2 points (and also your alcohol level by about .2% or so). It should have very minimal flavor impact.
However, if you completely forgot the DME and *only* added the LME and corn sugar, your gravity will be much lower than your expected gravity.
When it comes time to bottle either pick up some extra priming sugar or do I as I do and just prime with table sugar instead.