Need some help please. Any advice will be good to help me out.

I was sitting on the couch holding my 3 week old baby and I grabbed my phone with my free hand and all of a sudden it falls on my sons head. He cried a little and I calmed him down. There's no bump or anything badly just a light red mark. My question is should I take him to the doctors tomorrow to see if eveything is alright or just see how he does over night?