I just had this exact same issue as I'm also the first from my school to apply to UCAS. I went to my IB Coordinator, he let me watch as he logged onto the IBNet, selected "Requests for Results Service" page of the "Results" section. Then he scrolled down the candidates' names and clicked on mine. Where it says which institutions to send results to (it was already filled with lots of names of USA colleges from last year), he chose "Look up" to add a new institution. It looks like there's just about every university in the world. Among them, alphabetically in the U's, he found UCAS -- it's all written out University and Colleges Admission Service (or whatever UCAS stands for), he clicked that, and then it asked for the registration number, where he entered my UCAS number, pressed Confirm and it was done. This way IBO will automatically and electronically notify UCAS of my IB results, and UCAS will forward them to whichever universities I've chosen as my Firm and Insurance. By the way, this is the same procedure to add any American universities or other universities you might be applying to if you want them to receive your official IB results directly from IBO.
Note: the deadline for making this request is May 1st.
Good luck!