Your sister sounds amazing.
To your 20 year old self, I'd say - Is this what you really want to do? Do you really want to be here? Was there something else you'd rather be doing? If so, what is it, and go do that, and do it with gusto. Otherwise, make this happen, cuz it's the only "here" you got!
That's it dear, it's only now that we've got so we got to utilize our now and become better in the unknown tomorrow