2nd day after septoplasty, left nostril plastic film came out! Shall I go to the hospital? (photo)

It looks like you tore and dislodged an internal silastic splint from your nose and it would be best to see your surgeon asap. Refrain from nose blowing and instrumenting your nose/nostrils to avoid further difficulties. 

It appears that your surgeon used a silastic splint or perhaps gelfilm in your nose after septoplasty to help with healing. In some cases these are sutured in.
You definitely should discuss this with your doctor soon, but it isn't an emergency. He will likely want to examine the nasal cavity to make sure you are healing well, and in certain instances replace the gelfilm/silastic. It's unlikely that a doctor in the ER/urgent care etc, will be able to replace the stent and evaluate the recent surgery you had.
Best of luck!