As everyone else has says, you bid assuming that 2NT was natural and partner understood it as such. In that case, your double of 5H is entirely normal.
There seems to be some confusion here.
It depends what your partnership agreement actually is.
1. If your
agreement is that 2NT is natural then you are obliged to call the TD at the end of play (because you are the defending side) under 20F5(a). This explicitly takes precendence over the general rule that you do not have to draw attention to your own irregularity.
Quote
...The player must call the Director and inform his opponents that, in his opinion, his partner’s explanation was erroneous ...
It is reasonably likely that the TD will award an adjusted score with your partner playing in 4S on the basis that one of the 3H / 5H bids would not have happened had they known that 2NT was natural - although we'd need to see all the hands to be sure.
2. If you
agreement is that 2NT is Jacoby then you are not by law obliged to do anything. However, you must be pretty certain that you are right - because your partner certainly doesn't agree with you right now!
However, bearing in mind that "You're playing club pairs and a qualified TD and playing at a table with 3 players not so versed in the laws of the game..." it is definitely a good idea to explain to your opponents at the end of the hand something like
"... I thought that 2NT was natural, perhaps it would be a good idea to get the TD over..."
This post has been edited by FrancesHinden: 2008-August-20, 02:34