If you could write a note to your younger self, what would you say in only three words?
I had two thoughts. 1) Words can hurt. 2) Try your best.
What would your note say? 
Just Be Yourself
I would say not to give up on yourself. You are worth more than settling for easy.
Expect The Unexpected ( I have added that to the thread a long time ago. I do think its worth adding again)
Spend time in nature
I think about this a lot and since starting my journey 4 years ago, I've wanted to do a few things for my younger self.
Aside from giving myself a hug- here's a vague note to myself.
There will definitely be times where you can't handle anything anymore and you'll want to let go. It's okay that you feel weak. You're not required to be strong all the time. But I hope that you will find the courage and strength to share your struggles. I hope that you find the courage not to let go and the strength to continue on because there will definitely be better and happier times. These moments don't require any strength or courage, they just require you to be present, to be there- physically, not in memory, not in thought, but in person so that you experience these happy times just the same as you experienced the bad times.
(But then, I sound so preachy to myself so I just scrap all that and I'll just go for the hug.)
Itll be alright
Concentrate On Yourself
don't be naive.
Never Let Go