1) An ultrasound cannot do that. In fact, pregnancy is not often instantaneous. it would be totally possible, for instance, for any one of us to have, say, unprotected intercourse on Friday, and not become pregnant until Tuesday.
In addition, even if you had an ultrasound a month from now and were pregnant, if your doctor is using it to look at your appendix, he isn't going to be seeing what's going on in your uterus.
2) What you;re describing puts you at some risk, though without knowing your fertility cycle, or being there to really see what the contact was, it's impossible to say how much of one. Obviously, if your period is late this time, you should take a test.
You should also be aware that what you're described does also put you at risk of STD and STI transmission.
Editor and Founder, Scarleteen
My epitaph should read: "She worked herself into this ground."
-- Kay Bailey Hutchinson