I'm a big "plan" person too, so I can understand it being hard to let go of "the plan".
But, before you panic and try to let go of the plan, take a pregnancy test. If it's positive, then you need to come up with a new plan, which is scary, but you can do it. If it's negative, you might be able to stick with your original plan.
Don't stress yourself out with the "what-ifs". Get some confirmation.