Help with extracurriculars PLEASE!

So I’ll be honest, I have essentially none. My grades and scored are on the lower end of competitive and I know I’m going to need killer ECs to have any chance at my dream schools. It’s currently summer before senior year and all I have is playing guitar, a daycare job and volunteer work at the Science Center. None are particularly impressive in any way. What can I do quickly to really stand out?

OK, here’s the bad news:
Adcoms know this game. They know that a senior who suddenly finds EC interests is merely padding his/her resume. It’s not going to do any good.

So instead, why not adjust your idea of a “dream school” to schools where you have a decent chance of admission, just as you are? A kids at “the lower end of competitive” who plays guitar, enjoys the company and responsibility of caring for children, and who is interested enough in both science and education to volunteer at the Science Center?