If it’s closing, it’s most likely because of the honeycomb - the code is looking for circles, and the honeycomb is a LOT of them. If you cover the table with a bedsheet, towel, paper, cardboard, etc, it should capture properly.
We have this and a number of other tips here in the FAQ: Tips for calibrating / aligning the camera (and there’s a link on the bottom of that post with a few additional tips)