You might want to consider entering it as a Pale ale if you don't feel it will do well in the IPA category. I don't think seeing this as an explanation on an entry sheet would change my scoring if I was judging and IPA that did not have an adequate bitterness level. Flavor and aroma of hops in an IPA is a big portion of scoring, from what I am hearing from you is that this beer has this, but you feel it lacks bitterness. If you feel this than may be consider entering it as an APA.
But, when IBUs start to reach and surpass the human taste threshold, the hop flavors and aromas will take on a more prevalent role and the bitterness will fade or almost disappear. If you feel this is the case, enter it as an IPA, and try and comunicate the high levels of IBU's in the beer, and your hopping schedule. this might help guide the judges in their perception of the beer.
I would not recommend trying to explane to them what they are perceiving.