Don't Install If You Haven't Prepared
Don't install the iOS 9.3.3 beta if you haven't prepared for the iOS 9.3.3 beta. Simple as that.
You're going to want to do some prep work before you install the software. That includes making a backup (this could take awhile), learning about the downgrade process, digging into feedback about your particular update, and more.
We've put together a step-by-step process that will help guide you. Take a look, especially if this is your first beta.