You can use anything you want, no-one really cares. I've used break barrels with open sights before.
And if you don't want to, you don't have to have your card in at the end so no-one will see your score. But again, no-one cares what people score unless you are a big competition.

My first HFT event I shot a bog standard TX200 with hawke vantage. I didn't know my aim points/holdovers, didn't know the rules, and kept shooting the wrong targets. But it was mega fun.
Don't put too much pressure on yourself