You had it in correct, as you can see it will not go the other way. If that tube fits into it's hole in upper housing freely it will more than likely leak around it and definetely not stick.
Here is what I would do now that you have it off, is take fan belt off so water pump won't turn, fill as much coolant as you can get in right at the engine. Start engine and coolant should not move. If it rises up you have a combustion leak causing heating problem. You have to do this quickly as it will start to rise as soon as it warms so you have less than maybe a minute to take a look.