New to group and am a diabetic

Hi all, My name Judy and I am 71 years old.  I was recently diagnosed as a type 2 diabetic.  I  really like the app but was wondering why when I put in my breakfast, lunch and dinner and reach 30 grams of carbohydrates does it say I have none left.  I thought I could have 20 to 30 a meal. Any information would be appreciated.  Judy