I know exactly what happened, and I'm bummed out about it, but it's too late to do anything about.  What I'd like to know is, how can I prevent this next time?  Any advice?

This is my second cedar strip project.  The first was a SUP.  This one is a Petrel.  I did not have this issue on my SUP.  On both projects, I've used cedar from Home Depot (I know, don't judge), Raka 127/350 non-blush epoxy, and 6oz glass also from Raka.  Both projects were built in my climate controlled, basement workshop, so practically identical conditions.  As far as I can remember, tools and prep were identical as well.

I laid out my fiberglass, brushed out the wrinkles, got my stuff ready, mixed my epoxy, took a deep breath, poured it on, and spread it out with a rubber Bondo scraper.  Where I poured the epoxy on and it formed a puddle, I could see a faint outline of the initial puddle remaining as I proceeded with the work.  It's become less noticeable over time, but at certain angles and lighting conditions, I can still see it.  It passes the 10 foot rule, but it's still a little infuriating.

Since then, I've mostly finished the job.  I'm down to glassing the stems and final sanding.  Attached is a picture of the hatch cut out and sitting on my work bench where you can see the outline.

Also attached is a screenshot of Nick Schade's video from here: https://guillemot-kayaks.com/petrel/fiberglassing-petrel-deck-and-hull.  At the 1:50 mark, you can see the puddle he pours on the deck.  The outline of that shape (marked in red) is what I'm still seeing.