If you sell (go short) the put, your losses are potentially unlimited. You probably - I hope - meant to say that you were buying the put.
Guys, I'm shorting a put -- not the stock, not a call. The stock can go to 1,000 for all I care; I pocket the small premium, if it stays above 20. If it goes to 0, it's put to me at 20, which means I am down 20 -- my max loss.