Celebrating graduation the halal way

I just finished high school, alhamdulillah, and my grades were good too, alhamdulillah. Our school proms in the past weren't really Islamic – they had music, dancing, and immodest dress, which isn't how I want to mark my achievements. A couple weeks ago, our batch got together to talk about this year's prom. We agreed that anyone who doesn't want music can skip paying for the DJ. So I'm only paying for my certificate and to be with family and friends, celebrating our success together. When the music and dancing starts, my family and I plan to leave. But I'm a bit worried: since I'm paying for part of the event, could my money indirectly support free mixing between men and women? I can't control what others wear or how they interact. I intend, insha'Allah, to just celebrate without sinning – I won't talk to women and I'll lower my gaze – but others might not follow the same limits. Would I still be sinning if I attend like this, without paying for music, leaving before dancing, and avoiding any improper interactions?