middlename problem help!

I forgot to fill in my middlename on the application for naturalization. I never use it anywhere because its too long and hard to pronounce, but its on my greencard and social security card (not on my dl or back cards). INS sent me a letter saying i will need to provide explanation/proof of my name change and use of other name at the interview and they will send me what I need to bring. A couple of days ago I got my invitation to the interview and nothing saying about what proof i need to bring. What should I do? Is it bad? Can I just tell the officer that I forgot to fill it in and correct it on the spot?