Assuming you meant you turned it off immediately and waited 72hours. Good on you for doing so. However, I would not have turned it back on until I had cleaned the boards. I have fixed my nieces and nephews MacBook Pro since they are kids and spilt KoolAid on it. I would not worry about the rust issue too much since it is mostly aluminium (Aluminum does not Rust). To get it to turn off, I would hold down the power button until it goes off and not use it until you clean it with either suggestion. I personally use rubbing alcohol and it takes patience to ensure you have gotten it all.
Here is a guide on how to do this (although it says water damage the concept is the same) and should get you back up and running smoothly.
Electronics Water Damage (iFixit Guide)
Another quick sidenote: If you have a hairdryer this can be helpful in making sure everything is dry before reassembling. DO NOT USE HIGH HEAT SETTING as this may cause further damage, Low is fine at 6-8 inches from the components (your not trying to melt them, be cautious).
Best of Luck!