I'm not familiar with the Curves routine but is there a different group of muscles you can work on tomorrow instead of what you did yesterday and Tuesday?
Or...if you skip Curves, still do walking or ride your bike so at least you get some exercise in. I exercise every day and am lost if I don't. This time last year the only exercise I got was walking to the fridge!
Don't do anything that hurts you too much, that will defeat the purpose.
Good luck!