Alignment Problem with AMG 18s on 2000 C230

I just purchased a 2000 C230 and have put 18" AMGs with P235/40 ZR 18 90W tires and I have put on 1800 miles. My front tires are bald on the inside and my dealer is telling me I have to go to a smaller rim. Does any one know how to help me so I can keep these rims on this car.
Thank you if anyone can give me some info. email address is wirelessanswers@hotmail.com or call 319.530.2587