Hello dogbiscuit, thank you for your answer. It came from my haste of pressing channels while the pitch was still hot, I’ve made them too fast. I can remelt and repour this lap tonight if that would help !
Don't do anything yet. Mostly I was just asking Because I had seen 3 laps with much the same "extra channel" I was thinking it was an unlikely coincidence and maybe it was something shown or recommended somewhere on the web.
I don't know if that extra channel and very small partial facets at the edge are causing you any trouble. I'm somewhat obsessive about pitch laps. Of course I think anything less than a perfect lap might cause trouble.
See what Pinbout thinks.
If you were to decide to do something about it, or if you ever have a need to repair a damaged lap such as a severely chipped area and need to fill in missing pitch...
What I would do is scrape cerium oxide off the walls and floor of the two channels marked with red line and arrows. Then melt a small amount of pitch (from same batch) and fill those channels to very slightly above the top of the facets. With a razor blade, shave the top of the filler pitch to level with facets.
Cut another channel in the right place. Trim to reopen the crossing channels where melted pitch flowed into them as the unwanted channel was filled.
Press the lap.
I think the number of squares you have (except the extras) is good for a f/3.5. Larger squares might not flow as well as you figure close to the parabola. Overall I think you have done a good job making the lap.