Can I lie on the mat in jeans with metal zipper and buttons and with watch on my hand?

Better to have comfortable, soft, and natural underwear pants or pajamas. 

Lying on the mat would not be a problem as long as the metal piece (piercing, watch, zipper, ring) is not directly on the mat’s surface. So, please take it off or do not keep it on the mat. 

Also, be careful with metal objects because they can damage your mat, especially if you use the Purple Ereada® mat or Gemstone mat, where gems are fixed with the mesh fabric. It might be easy for you to catch and tear the mesh with your watch bracelet.