If the phone is too heavy, and the love you feel dissipates, return it and get another device, such as the HTC 8x or the Lumia 820 (if you still want Windows Phone 8). I suggest staying away from the Galaxy Note 2, as that weighs 180 grams, unless you feel that a device that's five grams lighter is just light enough to be comfortable.
In the mean time, try not to use the Lumia 920 too often in case of a muscle pull. If injury does occur, try using an ice pack on the affected area, and enjoy a nice cup of chamomile tea. Make sure you're fully healed before attempting to use your handset.