I’ll be honest, you’ll probably have trouble transitioning because (ignoring difficulty) Methods is very different to General. There’s very little cross-over so while you’re doing very well in your other classes, your results might not hold up – especially since you’d be jumping right into the year 12 course, not the introductory content that’s taught in unit 1 and 2.
That being said, I absolutely think you should give it a go. Because you’re only doing 5 subjects right now, there’s no harm in picking up another. Even if you do just enough work to pass and guess the multiple choice come exam time your ATAR will have benefitted at least marginally. I second Shadow’s suggestion of trying to get into it right now if you can. Alternatively (or additionally), try having a look at some past exams or one of the textbooks if you can scab it from somewhere so you can see whether or not you’d actually be interested in the content, and/or feel confident doing those sorts of questions.