Anna, I just knew it was an apple core you were hinting at! Are you hand or machine piecing this?
Can you give us a quick description of your technique or plan of action!
I tried an apple core many years ago and stopped when it reached the size of a place mat. I was machine piecing and the assembly had so much stop and start and pin and turn and this way then that way, I gave up on it.
The first row is so easy and then to add rows the instructions said to sew all the convex parts first and then go back to sew the concave parts as you sew each row. It was way to complicated for me back in the day. I would give it another go if I didn't have so many other UFOs to work on!
I really like this pattern and don't see it made much these days. I am happy you are doing it.
peace