Hosting a small-scale school tournament, advice?

[ZeroPixelHitbox]

This week Thursday, I am hosting a high school tournament, with approximately 21 people with a time limit of 2 hours.

The bracket and everything are done, but the kinds of people who are playing are 30% competitive and 70% casual.

What kind of balance should I seek? The competitive players will obviously weed out the casuals in an elimination tournament, so should I settle for a round robin?

Please help.

 

[JimmyTheCaterpillar]

Round-Robin would take waaay too long. That's literally 441 matches. How many setups do you have?
My first thought would to make it a Swiss tournament, but you probably won't be able to do that with one or two systems.

Honestly, I really don't think you can do a 21-man any tournament in under two hours without a lot of setups. Sorry, man.