Two spaces or not two spaces?

I've finally finished the first drafts of my three NSF essays. I must say, I really did not enjoy it. It's so hard to incorporate "broader impacts" into it all like they want. Writing these essays gave me a headache, which I still have.

And in this whole writing process, I learned that I have been wrong about something all my life. Apparently it's wrong to use two spaces at the beginning of each sentence! I've been doing this since I can remember, and now it's just second nature. It supposedly went out of style when they switched from typewriters (which use a monospaced font) to computers (which use a custom spaced font). I don't know what to think anymore.

I think I'll keep my two spaces, thank you very much.