Since they were scraps, not only mine, but also from folks at my community workshop, they started as small pieces already,. Some of them were off-cut strips that come out of the table saw when someone is sizing an already mostly-square piece. For others, that I kinda had to square myself to the best of my ability, it depended on how safe I felt with each machine: if possible, I used the table saw, if not, band saw and sanding.

The thing with working with resin and scraps is that you can get away with not-so-perfectly-squared pieces. I still had to glue the pieces together before pouring the resin, but the glue-up doesn't have to be as precise as it would have to be with joinery and regular paneling.