I failed a test and I hid it so my parents wouldn't find out.
Why were you afraid to show your parents the test?
I didn't want to get in trouble.
I can understand why you wouldn't want to be honest about your grades, but your parents will not appreciate you lying to them. It's only a matter of time before the school calls them and you get in serious trouble. You should tell them the truth right away.
I can pull my grades up before they find out.
You should just tell your parents so they can help you. Better to be upfront now than wait and let the lie fester.