I don't think you can ever be over cautious, even if the 'rules' say you can treat somebody with a specific condition or up to a certain stage in pregnancy, you are there and you are the only one who can access the situation, client, feelings you get - so I would say you did the correct thing if your intuition said don't do it.
I am not 100% sure but if I remember right from my classes we had to be careful and only give light relaxing treatments in the last trimester as not to induce. Actually, one of our fellow students was pregnant and she was practised on just as we were.
But, at the end of the day, I still think you're the best judge as to what to do, how much, how hard, and if you not want to to it at all. Being a good therapist at the end of the day is a lot about having trust in yourself, maybe next time you decide to do a treatment after more questions but then you will do it because you are comfortable that you have made the best decision you could.