I don't think you are being over cautious.
Take massage out of the equation, the standard recommendation is no major changes to normal routine in the first trimester, it is the most delicate stage of pregnancy, if something is going to go wrong, it's usually the first trimester, don't make major changes. That means no shift in exercise routine, no shift in diet beyond what might be required for managing morning sickness, they even recommend don't change jobs or move in the first trimester. So I just put having a massage in that no change to normal routine - if they are regular clients, I will still work on them in the first trimester, if I've never seen them before, I won't work on the in first trimester, add the fact people usually start looking for 'pregnancy massage' at week 10 or so, getting them to wait a couple of weeks is easy. I don't think a normal massage can set off anything that wasn't going to happen anyway (eg massage to bring on labour, they'll usually start labour in 24 hr or more than a week, it's as if it it was moving towards it in 2 or 4 days time it will accelerate it, but if it hadn't started progressing it doesn't seem to make much difference) Millions of people get a massage between becoming pregnant and realising they are pregnant without any ill effects, no miscarriage, no five headed babies. If massage in the first trimester was such an effective way to cause a misscarriage there would be no unwanted pregnancies, 'just press there!' would be known by many. I've got more faith in accupunture having an effect, but it's difficult for a normal massgae to stimulate accupuncture points to the same extent.
Having said all that, first trimester, if anything is going to go wrong in the pregnancy it's usually then and if something does go wrong, some people will look for any excuse, and since 'expert' text books and training say no massage in the first trimester, massage in the first trimester could very easily be implicated if someone was looking for something to direct the finger pointing at, the fact they'd been on a roller coaster, had an x-ray, eaten unpasturised cheese and been cleaning out the kitty litter can be overlooked and the massage gets blamed.
I've had a few odd enquiries where people are looking for a pregnancy massage very early in the pregnancy (4 - 6 weeks) when I said no they wanted fairly explicit directions of where to avoid, it was like they were fishing for information, so the public does seem to be thinking massage in first trimester can be risky. (if they are fishing I'll be vague with 'you need training to know all the spots')
No massage in the first trimester is for the protection of the therapist, not the client! Are you being over cautious? For your sake no, for the pregancy's sake, probably yes.