I have a Jeep Commander 2006 my rear sensors go on everytime i back up??HELP?

i hit the car when i was going backwards because i did not see the pole it was below my car. I did not damage the car there is a little tiny dent and a scratch but everytime i back up and there is nothing behind me the rear senor goes on. I am 18 and my dad let me use the car and i need to fix it before he comes. i also dont have insurence!