This dream is full of odds and ends to explore. Let's take it apart as best we can.
You built a machine. To invent something in a dream is directly connected to your personal creativity. Here, you not only created something, but felt the need to test it—and it worked! This part of the dream, then, is about your aspirations, your hopes that whatever you do will be successful.
Let's not overlook, however, the fact that your dream showed you to be a student. Deep down you still feel you have things to learn. And you also had a professor, someone you were eager to report your success to. Without more information, this person (in the guise of Bill Weasley . . . from Harry Potter?) could represent anyone: a parent, a boyfriend, an ex-professor from your college days, even an aspect of yourself to which you feel the need to prove (to yourself) your abilities. These are all viable possibilities. But the fact that he worked in the same field as you (I'm assuming, since you were working for/under him?) suggests Bill may have been standing in for someone you admire, someone who you would like to emulate in your own creativity and/or career.
Unfortunately, your path to Bill, whom you would very much like to impress, is fraught with peril. First you are detained by sorority girls dressed in pink. You say they were "rambling" which indicates some frustration on your part. Here the girls almost certainly represent all things quintessentially feminine: they are part of a girls' organization, are dressing in the color most associated with being female, are chatty as women are often said to be. You show impatience with this aspect, bordering on rejection. The question you must ask yourself then is whether you are in touch with your feminine side. Are you perhaps lacking some balance there?
Yet you leave these girls to fight off a monster. Interesting. Your dream doesn't say whether you felt they were at all capable of doing this. Have you abandoned your femininity and left it to fight alone in some way? It's a man's world, as the saying goes, and since this dream skews toward your personal ambition, perhaps you've embraced the more masculine aspects of the working world?
More obstacles arise in your quest to enlighten and impress Bill. Instead of waiting your turn, you decide to take the shortcut. Instead of attempting the rickety bridge, you opt for the muddy water. There's a lot being said here. You're looking for quick results. You're not convinced the standard way of doing things—the bridge everyone else is using—will get you there safely; it's wobbly, possibly not stable. Others are having difficulty with it. You feel you can move faster, and even more securely, by wading into the river. It's dirty . . . Water in dreams symbolize emotions. The others in this dream were staying above their feelings, perhaps remaining logical. You went right into the water, however, immersing yourself (at least partly). And the water is dirty, which can mean your emotions are a bit unclear at the moment. You don't say whether the river was moving quickly or not. If it was calm, that indicates you are more willing to "go with the flow," but if it was rapid, it signifies you feel a tad out of control about something.
The fact that you stop to take someone's hand, though, suggests you're willing to make that connection with higher reason and logic. And that you're also willing to connect with others and help them if they need it, even at the expense of your own goals.