No you are completely fine! If you touched semen on a surface chances are it was already dead outside of the body semen does not have a long life expectancy. I would just make sure that you are not touching semen and then touching yourself right afterwards if you want to avoid like cdawg199 sid stds or pregnancy bc although its highly unlikely it can still happen theres always that chance. Hope this helps let me know if you have more questions. I hope everything works out :)
No, you have nothing to worry about.
However, if you were engaging in sexual contact w/ a male friend immediately preceding you inserting your fingers into your vagina & that sexual contact involved him having ejaculated semen - if any amount of that semen was on your fingers when you were fingering yourself, it is possible to become pregnant or contract a Sexually Transmitted Disease (STD) as a result.
Though, if as you say it had been a long while since you "may have touched a surface that may have/may not have been touched by a male schoolmate who may/may not have semen on that hand" then you have absolutely nothing to worry about from masturbating, it should be an activity you enjoy in & its exploration can teach you a great deal about yourself as you mature.