I can understand your concern. Anyway, the way you described is quite a low risk one. But still the risk is there. Studies show that sperms contained in pre cum is also sufficient in making a female pregnant, if it is getting chance to fertilize an egg. Sperms in pre cum can survive inside the favorable conditions of vagina and vaginal canal. Now, you may rely on an emergency contraceptive or just wait till your next due date of periods. If it is not occurring take a home pregnancy test to rule out the possibility of getting pregnant. Hope I have answered you well. Good luck.