Infused a flat panel for the 1st part of my dash, and have got some small slit like marks in the resin.

Unfortunately they don't show up when I photograph them - very small little slits, 5mm long max, and about the width of a letter l.

I'm thinking I didn't shut off resin long enough before the vacuum perhaps ? and they are air bubbles ?

Any ideas ?

As Hanaldo said, it does sound like voids

Make sure you entire stack of materials has wetted through prior to clamping-off the resin feed, even if it means a little resin finding it's way into the catch pot.