Asalamualikum if someone follow opinion that it's mandatory to fill 1st row before making a 2nd row for salah. What to do if you come late for salah and you see a gap your gonna fill, but it will disturb others as your blocking one of the exits and 5-10 people are waiting for u finish your salah?

Ustadh AbdulAziz al-Haqqan

The salah is valid on each view. And the jumhoor (majority of the scholars) are upon that it is an emphasized sunnah.