I haven't sewn my finger...yet. But I have stapled my thumb. While talking to someone, I mindlessly open the stapler, but my thumb under it & used the other hand to slap it. It was ouch alright. Now, THAT IS an idiot.
I must have thought since the bottom isn't on, it can't staple, forgetting that the staples are in the upper part and the lower part is only for bending the staples themselves.
In addition to the tetanus shot, keep it saturated with Neosporine (or a generic) to prevent an infection & speed up the healing.
Sew sorry it happened :(