I have travelled from Muscat to Riyadh for totally 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?

If your statement of 90 km is correct, then your prayers are qasr.