HELP WITH EXHAUST SYSTEM PLZ

Hi there guys and galls- this is prob an easy one but im new to scoobies.

I have recently bought a performance middle section and back box for my 02 wrx bug eye

here is the exhaust system that i have bought

01-06 Subaru Impreza 3" Catback Exhaust WRX STi 02 03 on eBay, also Exhaust Components, Performance Tuning Parts, Car Tuning Styling, Cars, Parts Vehicles (end time 15-Feb-08 21:55:43 GMT)

I have taken this to a garage to be fitted.
But i have been informed that the middle section does not fit my standard downpipe?
Just wondering if you guys can help me.
Just od not want to buy the wrong item.

Thanks