I used to show AQHA, and (at least in my area) people didn’t really use hairnets/stuff their hair into their helmets. So I always just put it into a nice, tight and low bun. Occasionally with a hairnet over the bun to keep any stray hairs tidied up. It can be a little tricky depending on how far down your helmet comes, but as long as it’s neat, with minimal flyaways, I don’t think it matters much how you get it into a bun (braiding, twisting, gently “squishing” like a ballerina bun, etc).
The last show I was at I somehow managed to cram all my hair into a hairnet and under my helmet, but honestly, it was so much harder to do (my hair is quite long), and I think I’m able to keep it neater and nicer looking in a bun anyways. Just bring a fine tooth comb to lock down any flyaways near your ears with lots of gel and hairspray.
edit to add: Depending on how long and unruly your hair is, you could probably braid it tightly and tuck it into your shirt collar before you go in the ring. It might not be the most comfortable thing, but then again, neither is stuffing it all in your helmet.