While I'm not sure what the reference ranges mean for the test that you have, I can interpret the answers for you.
The rubeola and mumps titers simply mean that you have good immunity against both of those diseases. "positive" is really all that matters. The titer itself does not, and can vary widely from person to person. Simply put, when you received the vaccination as a child, you launched a great immune response to it, and in fact, it doesn't sound like you NEED a booster for either of those two diseases. You're well-protected. Congratulations!
For the rubella, if "26" is not "positive" according to the reference range that you have, it means you may NOT be protected if you come in to contact with someone who has that disease. It's pretty rare, but it is dangerous, although mostly only to pregnant women. However, I have certainly seen a number of patients who are NOT rubella immune, although the only time we check is if a woman is pregnant, or in your situation, as you go back to school.
My recommendation would be to get another rubella booster shot. Not sure if you can get the shot without the Measles and Mumps in it, but if not, getting those vaccines again won't hurt you, although we've already mentioned that you don't NEED them.
More info can be found at the following website: