Zen, The 5" of reflex is too much strain for that design and wood combination as well. Usually an inch of net reflex in an r/d design can put your bow at the top of the speed food chain
Like mentioned it may have still been wet from the steaming..
These designs hold their shape better if the belly is floor tillered first and then glued up in the desired shape. Plus r/d profiles take a lot of experience to really get the performance out of them.. Much of wood bow speed is also derived from the archers skill as well, and a good on with a straight bow will outperform an average one with a tricked out bow.
If your red-oak board is straight enough for a self bow I'd try to make a few of those to get experience.. When learning, tillering lots of bows is key to developing the skills needed to be consistent and knowledgable.
Rich