Hi Bonnie! Great advice from Robert. Using less water is definately better - keep your very wet loose washes for paper that you've stretched not your sketchbook.
I have "ironed" pages in my sketchbook if they stay really cockled. I place a clean piece of white photocopy or printer paper either side of the one that is cockled and use the iron lightly (no steam!) keeping the iron moving constantly. I've had pretty good results so that the book closes flat again.
Hope to see some of your work in the forum