LT way off in race??

First and foremost:  CONGRATULATIONS on your first race!  That's awesome and welcome to the sport (it is crazy addictive).  

I suspect you already know some of the issues that can come up, based on the excellent questions you ask.  Now, I'm no coach, but since this is Beginner Triathlete, I'll at least give my experiences (to be taken with hearty grains of salt).

Your LT could have indeed improved.  So that's great!  Buuuut, not likely THAT much in so short a time (some but not all of the difference).  So, on to some other possible contributors.

I see a considerable difference between the power I can hold on a trainer and on the road.  Cooling, road feel/interest, mental fatigue, subtle changes in body position on the road that you don't get on the trainer but that help keep you "loose" and such can lead to differences.  Retesting on the road will help, I suspect.

I also see a goodly difference in what I can hold during a test and during a race.  I can peg the redline and hold it there a LOT longer in a racing situation that I can if I'm just out doing a test (in s/b/r - any of them) on my own - no matter how hard i THINK I'm pushing myself.  Maybe I'm mentally not strong enough to really hammer if I don't have a number pinned on my chest, but there you go.  

If you're a fit athlete from other endeavors, your zones might also be somewhat "compressed" toward the top end of the range.  So, your threshold HR might average a higher number than the method you used to calculate it might have.  The more fit I get, the narrower my zones and higher the HR numbers...

The other source of noise could be the HR monitoring equipment, but I'd put a lot less emphasis on this one and more on the two above (iow, not likely a meaningful contributor).

If you really get into the data and have the discretionary funds (two big if's for a lot of folks), using a power meter on the bike can be a very helpful tool in setting zones, both for training and racing.  I'm sure a few other folks who are much more knowledgable about that will chime in here (I'm about 18 months into using mine, so still learning).

Just my tuppence/experience.

Again, congrats.  Sounds like you're hooked, which is terrific!!

Matt

This^^^

Your zones are likely bit off.

Many when first test don't execute the test well. It takes time to learn how to suffer and push yourself. A race environment brings that extra incentive to suffer and push.

Congrats on your first race.