SNAP. That's what happened, I reckon.
Tried again today. Poured the resin into a glass container, mixed well, few strokes with the brush to leave a nice coat. 5min rest prior to putting it outside (cloud). 15min exposure to UV gave a nice shine on the surface but bit tacky still. Massive improvement from last time, but I blame the weather for the marginal tacky-ness.
after 30min out in the UV, sanded with 80 grit initially to get rid of the tacky surface, then 150, 180, up to 400 no problem. Came out nicely. Not perfect, but good enough for my satisfaction.
I think I'll stick with resin + catalysis than UV resin. Though I'm on the sunshine coast, the sun doesn't come out when it's most needed...
Thanks once again for all the tips.