I would say it is incorrect, yes.
If you ‘emphatically occupied the meeting room’ it would mean that you moved around in it a lot, in an emphatic way, making lots of gestures.
I don’t think that that is what you mean to say!
‘Emphatic’ usually relates to a ‘form of expression’. It is the expression that is ‘emphatic’.
You could, however ‘be emphatic’ in your refusal to give the room to someone else. As in:
‘My refusal to leave the room was emphatic’.
Note that here, we are again referring to ‘your expression’ your ‘refusal’ is ‘your expression’ - ie your gestures, speech etc, which, being ‘emphatic’ - are emphasised - meaning ‘forceful, exaggerated or larger than life’.
‘I emphatically refused to leave the room’ is also ok - note thst it is the refusal (the ‘expression’) that is emphatic.
Again, if you try to say ‘I used the room emphatically’ it is your ‘use of the room’ that is emphatic - so here we imagine you prancing about in the room theatrically, making overblown gestures and speaking loudly.
‘He was emphatic in his occupation of the meeting room’ does work - but again it is ‘his expression’ that is ‘emphatic’.
Another way of saying that you used the room forcibly might be:
‘I camped out in the room, without permission, emphatically refusing to allow others to enter’.
Or, ‘I subversively occupied the room without permission, emphatically fighting off any would-be intruders’.
Hope that helps!