It sounds like your printer is pulling the pages wrong. You need to print it just as it is ordered in the pdf. If your printer isn’t choosing correctly, it’ll be off. To ensure it’s correct, print pages 1-12 first, then print page 13 by itself. This may sound obvious but Page 13 (last half of dec) must be blank on the back.
Once you print and trim, you'll need to place the months in the correct order.