The first obvious thing to check is that you are actually teaching things in the best possible order. It takes a lot of courage to admit being wrong, especially in front of students, and when one is in a position of authority. It's my opinion that one of the worst things a lecturer can do is lean on their authority to save face, e.g. "It might be wrong, but it's my way!" I still remember the college professors who pulled that, and still hate them for it.
You said that you checked with your colleagues and you are justified in doing things the way you do them for pedagogical reasons (the fact that last year's syllabus did it one way is no reason; the syllabus can be wrong two years in a row.) So I'll assume that you are correct.
To teach effectively, one needs to adopt the difficult position of the benevolent dictator. You need to create an environment where students feel free to question you about anything and everything, and this is OK, because being the expert in the room, you should have an answer to everything and anything they throw at you. Even if the answer is "that is outside of the scope of the class, but if you come to my office hours we can talk about it." So when a student claims that they know a better way to teach the class, you just need to calmly explain why you are teaching it this way, and how it is to their benefit. Then you move on. I'm going to call BS on any student who says they are talking on behalf of the class -- they are just the loud ones, and if your explanation is reasonable, most students will silently agree with you.
Back to the benevolent dictator metaphor, part of your responsibility is also to keep order in the class. Some students, usually early in the semester, try to poke holes in your authority, and if you let them there's no way to get your authority back. They'll go to the chair of the department, and then to the dean and then to the provost over the smallest of grading disagreements. And being an adjunct, there's a risk that somewhere along the chain of command someone will say "this guy/gal is too much trouble, don't renew the contract." So paradoxically, to keep your job you have to be stern, especially at the start of the semester, establishing your authority.
Just to be on the safe side, you can go by the chair of the department and check with them if they agree why you are teaching in that particular order. Something along the lines of "I am OK with teaching it either way, but I think this way is best for the students because of this. What do you think?" When that student, the one complaining in your classroom, inevitably goes to the chair to complain, they'll get their ass thrown to the hallway, and you've re-established your authority in the classroom.
There's always a risk that the department will not back you up, but it's also impossible to teach without authority. Students can't run the classroom. I once taught as an adjunct, and a student kept not showing up for exams and then demanding a make-up. I let it happen once (thus undermining my own authority), and then the student kept demanding it for every subsequent exam. When I tried to stand my ground, the student went on to complain up the chain of command. I knew they were complaining, but I never heard anything from the department other than my contract was not renewed. I took two lessons out of this: (1) I did this to myself by undermining my own authority early in the semester (breaking my own rule of no make-ups unless you're at the hospital) and (2) I don't want to work at a department where they don't back up their adjuncts.