For the future, if you are traveling with someone you know (or if you know that your flight is going to be quite empty), you could put it under the seat in front of you. I've done this a number of times with a full size carry-on for PIT-YYZ and YTZ-YUL flights, which tend to be quite empty, or if I have a super tight connection, and have an empty seat next to me. Personally, on the flights I've been on, the FA's were OK with it, but I can imagine that not all would be.