Pretty much no, you're unlikely to offend anyone.
I suppose you could end up with an unfortunate faux pas if you used the expression specifically in relation to LGBTQ matters, and if you were saying that it was them who had been "set straight", though it would have to be a really unfortunate phrasing.
If anything, it's just as likely to be used humorously as part of a pro-LGBTQ statement as anything else. In fact it very often is. Too often, just on the "it was funnier the first time" count. I'm pretty sure Navratilova used it jokingly when she came out in 1981. That was over 30 years ago, and it's not like she was the first.
So yeah, if you're actually writing a speech for Pride or something, please try to think of a more original joke.
But "setting straight" when it's you who was "set straight" by them is going to be pretty safe, unless it's said with some sort of sneer.
For all that, if you don't know them well, and it's a short communiqué like an e-mail (notorious for losing nuance), then your edit was perhaps a good idea, just to be completely on the safe side. Still, I wouldn't bother. It's just that in any case where you think something could be misconstrued, then it's always safer to rewrite than not rewrite, especially in short messages, whether you're wondering "is there a chance of this being misconstrued in a way that gives offence" or "is there a chance of this being misconstrued as tomorrow rather than the next Wednesday", or whatever.
Really, the word straight has so many well-known useful senses that those of us who are queer can't really get by with only using it to mean heterosexual, so we generally don't expect straight people to either.
For that matter, if there was one sense in which I would like it to be magically removed from the language, it's that meaning of heterosexual, given that so many of the other senses are positive in relation to an alternative. But since there really isn't any alternative non-pejorative informal term for heterosexuals of similar currency, that's not going to happen any time soon.