Baking sode will not hurt your teeth, especially when brushing. Before the invention of toothpaste, folks brushed their teech with baking sode and many still do. Baking soda is used like a light abrasion for the purpose of cleaning. Normally, mix baking soda with some lemon juice. The lemon juice acts like a whitener. I suspect that baking soda has an expiration date, like everything else.
If you don't have any pain or swelling on your lip, then you should be okay. It would be a very, very good idea to buy a new box of baking soda!