I have travelled from Muscat to Riyadh for a total of 13 days at 2 points. Point A is on the outer side of Riyadh. Point B is in Riyadh City. I have stayed at point A for 8 days and point B for 5 days

Both points are atleast 90 kms away from each other

So will my namaz be Qasr for the entire trip for 13 days?

Yes you have offer Qasr Namaz because your stay is in two different places for less than 10 days.