Class/lesson/future

Tomorrow we're watching a musical in school which will be taking about 3 hours. So we only have one lesson tomorrow. Can I say it this way:

We'll only be having one class tomorrow.

And in general, what do you say if you have to go because you (have/are having) your (class/lesson)?
I'm off to class?
I'm having my class now?
I have my class now?
I'm having my lesson(s) now?
I'm about to be being taught?
I'm being taught now?
I'm about to have my (class/lessons)

There is hardly any difference between class and lesson(s), is there?

One more question: What's the difference between present continuous for the future and future continuous:
I'm watching a film on Friday.
I'll be watching a film on Friday.
I'm working this evening.
I'll be working this evening.
I'm meeting you tomorrow.
I'll be meeting you tomorrow (Is that correct?)

And one more: With the verb 'to be', we also use 'present continuous' for the near planned future? Or do we take the going-to future? (For example: A: Mum, May we learn together tomorrow? B: No- I'm being at the hairdresser's tomorrow - or - I'm going to be at the hairdresser's)