Very Quick Standard Deviation Thing

Sorry, I haven't taken stat yet, and don't know how to properly interpret standard deviation (I'm also aware that there are a few different definitions, so I'm getting myself confused).

Anyway, I want to have a good error on my earnings/game on heads up SnGs, so I calculated the standard deviation as sqrt(p(W-E)^2 + q(L+E)^2), where p is my win % in decimal form, q = 1-p, W is amount won when I win, L is amount lost when I lose, and E is my earnings/game. This was nice, except that I don't know if it's the standard deviation per game or standard deviation of total profits or just not what I'm looking for.

First answer gets a cookie; sorry for wasting your time.