Maybe this term "Risk" should be used when we are ready to lose certain amount of money, or in other words - when we have SL and the combination of lot size and stop-loss results in predefined loss. When you have 0.03 Lots, you can close the trade when it have 3 dollars loss or 300 dollars loss, or any other loss.
Anyway, I will suggest this option % of Balance => Lots. The calculation is very similar to yours. If you have 1000 dollars Balance, then 100% means that the lot size will be 0.01 lots (because 0.01 lots are 1000 dollars when 1 lot is 100,000 dollars). So instead of 3, use the value of 300. And note that this option will work on EURUSD and most currencies, but for fancy markets things can be a little bit different, because everything depends on what is the size of 1 lot.
Or you can also build your own formula and use it directly. I'm doing it that way sometimes, it's actually easy to use some native MQL4 values like this one: http://docs.mql4.com/account/accountbalance
This was some calculation that I personally used somewhere, just for an example, it only means something for me: http://prntscr.com/76t4e8