Gina,
How long have you been training your abs? The balance ball routine is very intensive. It works you much harder than ab routines on the floor or on a bench because it requires balancing in addition to the movements. Statdeac's suggestion is the best I know of for stretching the back and abs.
Muscle soreness is part of the game, sometimes. I have found that it normally takes 21 workouts for me not to get sore when trying a new routine. If that holds true, it will be 2010 before my 'biking muscles' stop hurting.
Travis