Start of the Rainy season, and I'm Learning Japanese....NOT!

The rainy season has begun! Rain came down in waves, thunder shook the school, the lights flickered. The rainy season made a dramatic entrance. I learned the term zaza which is the term for when "it's raining cats and dogs."
Apparently I have been Borating all my coworkers. In Japanese there are many levels of formality, words subtly change depending on the formality level between people. In general the more formal, the longer the word. (Example to Ben I would say onegai (please) to a coworker I would say onegaishimasu (please) to my boss I would say onegaiitashimasu (please)). I thought that the phrase janai made things more polite;  I was wrong. I have been using it liberally to try to be polite at work. It basically means 'not'.
Many people asked me "Do you like the Sakura?" I emphatically responded. Hai, ski de wa janai! Yes, I like the flowers...NOT! I tried Jedi mind tricks on all the people who asked me if the books I were holding were mine. Hai, watashi no hon de wa ja nai. Yes, these are the not my books. People looked at me in very odd ways, I knew I was making mistakes, but I thought the janai at the end would let them know I was sincerely trying to be polite. Ooops! I have learned that the people whom I work with are incredibly patient with me, and I am very grateful for that. Hopefully by the time I leave, I will be able to tell them clearly how grateful I am for all they have done!