I am taking a Spanish(*) course with a private teacher and they were on vacation these days. Since I was not totally sure whether my teacher was back from their trip, I sent a message today to check if there is a class this coming Saturday. Among other things, I wrote
I was not sure when you were coming back from your trip.
My teacher corrected me and claimed that
I was not sure when you would come back from your trip.
should be used.
Which sentence is correct? If both are correct, do they differ in meaning?
I think that the second sentence expresses more uncertainty than the first one. Am I right?
(*) the whole exchange was in English. I am only mentioning the Spanish course to point out that none of us is a native English speaker.