Re: your last name is Khan, really?
There were many Pashtuns who brought the name Khan to India when they settled in different Indian cities. People like Josh Malihabadi (Afridi), Mushtaq Ahmed Yousufi (Yousufzai), Maulana Muhammad Ali Jauhar, Dr. Zakir Hussain; all had Pashtun background. A lot of them opted for Pakistan alongside other Muslims when Pakistan came into being.
So it is not surprising to see the surname Khan among Urdu speaking people of Karachi.
Secondly, Khan Bahadur was also a title awarded by the British government. Thus many people with non-Pashtun background also have the Khan surname.