Yes, you hit the 100,000 point maximum and will not be able to earn Amtrak Guest Rewards points from your account usage until the cycle restarts. The annual cycle is based on the date your Amtrak credit account was opened with MBNA. The following is from section 1 under the terms and conditions listed on the online MBNA Amtrak Guest Rewards application:

"There is a Yearly Limit to the number of Points earned through use of the Card: Platinum Plus Cardholders earn up to 100,000, and Preferred Cardholders earn up to 50,000 Points. The terms of the Program are subject to change."