How can I be more forceful to get things done?

So I'm having a quinceanera and we had to drop our dance teacher recently and now I'm teaching the dances

I'm having a surprise dance and a waltz

I already made the surprise dance a long time ago and it's easier teaching this dance cuz im only teaching the girls part for now, but for the waltz it's hard to teach the guys and get their attention. I've been told a lot that I'm 2 nice but then when I try to take control ppl won't really take me seriously

What can I do to b more forceful yet still be kind instead of being rude? We only have so much time til school starts and we'll have to have less practices when it starts.

Any advice?