Hi, and thanks for your medical question on eHealth's Ask a Doctor forum.

If your partner ejaculated on your hands and you dried your hands most of the sperms would die when exposed to air. So if masturbated later with the same hand there would be no viable or live sperms to cause pregnancy. Hence there is almost no way you could become pregnant. This does not need one to go for Plan B pills.

However as a matter of abundant precaution, if you miss your periods by a day also take a pregnancy test. Hope this helps. Take care!