Could anyone please tell me where I am going wrong with this boost converter?
I'm going to necro this thread, because I had a similar problem and it may be useful to anyone googling it.

My application did not have any current limiting hardware; this one should. But the possibility exists that the series inductor value is lower than expected, which would allow an unusual amount of current through the onboard switch. 

To find out, you could use external switching transistors that can handle it, in a cascode configuration.  Or, a gate driver IC and a Mosfet.

If the controller IC still burns out after that, you may have a bad batch of controllers. This happened to me recently, where the ICs I had ordered had been damaged at the warehouse.