Backing up your site?

Hi,

My site is not yet live but will be live on the 25th of April. I’ve spent SO much time getting it perfect and then I was hit with the terrible fear, today, of what if something goes wrong and I lose all my changes and content?
I know nothing about making websites (though I did a pretty great job with the one I fixed up :)) so maybe this is a baseless fear. But am I supposed to/able to back my site up somehow?

Thank you.