wow, relax. 2 weeks is plenty of time. when i found out i got in for first year i had to fly out 2 days later!
you can easily get tickets for 2 weeks later. it's highly unlikely that the school will change the start date. everything in Pakistan gets confirmed at the last minute -- this is just your first experience with it. the best advice i can give is to just roll with it.
oh but British Airways has currently stopped flying to Islamabad, in the wake of the Marriot hotel bombing...so yeah try Etihad -- it's a really nice airline and the food is pretty good!