Trust me.
Everything you write is worth it. It doesn't need to have the best grammar, or be epic poetry, or the greatest story since "Half of a Yellow Sun". Write it for yourself. You will only get better with each thing you write, reread and revise. Your first may not be any kind of masterpiece, but it will be just as important as one. Open it up years later and you'll discover more about yourself, than you could ever believe.
I remember when I had a diary in secondary school. I read it up the other day, and I couldn't stop with the feels. I laughed, i felt sadness, i blushed, i felt things i thought had been hidden away.