Related for Menachot 82:18

R. Shimon says: One may have a bed, a chair, a bench or pull up a chair on the Sabbath; and one don't even have to say: on a holiday.

The number of the Tzitzit threads on all corners is 4 strings folded over, which is 8. If more were added, they are invalid. You should trim the tips of the 4 threads then insert them in the corner. Finally, double them over and then there will be 8.