ANSWER:

What your father has said is totally wrong!

It’s highly recommended to keep the balance between left & right side of imam but if it’s not kept, this is going against the highly recommended sunnah but this does not invalidate the prayer 

QUESTION: In my masjid there is imbalance in the rows. I mean there are 8 men on left side and 15 men on the right side from the imam. My father stops me from joining the row where there is imbalance and calls my prayer null if I join prayer on that side. Is my prayer null or can I join the row where there is imbalance?

Prayer |