You’re right — 37 faithless electors would deny Donald Trump 270 votes (he’d get only 269), but it would take 38 GOP electors switching from Trump to Clinton to give her 270. 37 would only give her 269, and the game would end in a tie that would go to the House.
However, that’s pretty moot, because in the past century, there’s never been more than one faithless elector in a given election, and even that has only happened nine times out of 25 elections. Previous years saw more. The record is 63 in 1872, and that was only because Horace Greeley, for whom those electors were pledged, had died between Election Day and the day the electors cast their ballots. But except for an election when one of the candidates died, no election has seen 37 or 38 faithless electors. And even if there were this year, the chances that 38 Republicans would jump from Trump to Clinton when they’d have a chance to vote for another Republican (thereby giving the House an alternative Republican to make President) are pretty darned slim.
On the other hand, pretty much everything about this election is unprecedented. Be prepared for anything.