Was I wrong in telling my girlfriend she gained some weight?

First i want to say my girlfriend is not fat. She did gain some weight, but not like a muffin top or anything like that. 3 days ago i said "you packed some pounds", i'm a joking type of guy so she thought i was joking but i told her that she gained some weight in all seriousness. I told her it's not a big deal but just letting her know. Then all of a sudden she got emotional and to my surprise she was saying how fat she was and if i still loved her and just dumb things like that. Of course i told her i loved her, and told her that is not fat but she gained some weight. The past 2 days she has not been the same, she doesn't really want to hangout with me and earlier today we went to go eat out and she said she didn't want anything, I thought she was kidding but she literally took nothing. I told her to just forget about what i said. I know the food she liked, so i ordered it for her but she still did not eat.

Was what i said bad? I want her to eat and not starve herself. When i told her if she's eating proper meals she said "it's none of you business". I never knew she was that sensitive. Again she is not fat but just gained some weight. What can i do?
Was I wrong in telling my girlfriend she gained some weight?
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