Since you're short the put, you'd have to buy it back in order to close your position before it expires. If the put currently sells for $21, then you would have to pay $21 to close your position. So in a manner of speaking you "owe" this amount. Since you received $41 in premium and you can close out your position by paying $21, you have a paper "return" of $20.
It's the opposite effect of buying an option, where your "return" is what you can sell it for minus what you paid for it. So if you had bought the option for $41 and it currently sells for $21, the "value" of that option is $21 and you'd have a return of -$20. Since you're short, the "value" is negative (you'd have to pay $21 to close the position).
If you hold this position to expiry and it closes out-of-the-money, you will "owe" nothing and your profit will just be your premium. If it is in the money you will have to either buy the put back to close your position, or let it settle, buying the stock at the strike price with your cash margin. Since you bought it for more than the current market price, you'd have an instant "paper" loss.
how is my return anything less than $41 if share price is above strike?
Remember that "return" is what you received in premium minus what you will owe if the option is exercised (or what it costs you to buy it back). Your return at the time of opening the position was 0 (ignoring any bid/ask spread) since you could just buy the position back for what you received for it. If the price of the stock has gone up since you sold it, then the put (all else being equal) would be worth less, so you can buy it back for less than you paid for it. Your "return" will never be more than $41, because the lowest possible value for the put is $0, and your only profit will be the $41 you received in premium.