it could have been a mix of light leak, bad exposure.
i don't know to be honest, seeing i wasn't there, and have never
used fuji film or any film that was asa 3000 ...
what you might do is set your electronic camera to asa 3000
and make an exposure WITHOUT a flash and see what
your camera said the exposure was. expose your LF camera
with your instant film at the same settings.
use your camera as your flash meter ( if you don't have a meter )
you should hopefully get an image on the film.
hate to say this, but the learning curve for instant materials is kind of steep too
gettng a couple of tupperware trays for dev + fix + water
will give you instant results without the hassle of wondering
if our instant film is bad or your lens isnt' fast enough + fstop isn't smallenough
and the chemistry + materials might cost less than 4 exposures made with your instant ...
good luck !
ps. asa 3000 is like surveillance speed, it needs very little light to expose it normally.
a flash, even with a lens stopped down to f45 would be way too much light.
when i did newspaper work years ago, i used a 200ws lumedyne head, and asa 100 tmx
and at 6 feet on a normal day, or normal interior i was stopped down to f 22 at 125thS
i have a feeling your flash was way too hot and your film way too fast ...
get rid of your flash, and shoot in soft low light you might be better off ...