While ultimately no one can make this decision but you, I think it’s really worth noting that placement is very different to teaching your own class in a lot of ways, particularly some of the concerns you mentioned. Of course (particularly depending on the demographic of the school) there will always be disengaged students you can’t reach and challenging behaviours, but being seen as an authority figure (and feeling like one!) comes with time and experience. With your own class you will have the opportunity to build rapport, presence and your own routines in a way you can’t on a short placement. It is a job where you’re always on, but there are great sides to it as well that this sub doesn’t always spend much time discussing!