Hey Breezy nice to read your first post.
I was 14 and not baptized when I completely stopped doing anything JW related. I simply told my mom the truth - I didn't think the JW religion was God's organization and I no longer wanted any part of it. It took a while for her to realize I was determind to stick with my decision but she finally relented- and she is a complete zombie fanatic.
As a non baptized publisher you have nothing to fear and your mom will eventually come to terms with it as I can bet you she'll simply spend her years hoping you'll return while at the same time no one will be required to shun you so you will still be accepted as part of the family. Since your dad doesn't seem angry it is highly unlikely you'll be kicked out of their house. For a while there will undoubtedly be some tension but as long as you stay a good, respectful and responsible adult, it will eventually fade and life will adjust to the "new normality". This is a great opportunity to show them one does not have to be a JW to be a person of substance and a good example.
Keep us informed!