Having a problem with my exhaust system

[LP1029]

I have RMF headers that are 3 inches in diameter but the test pipe doesnt fit becuase its a 2.5 inch diameter whats the best way to make that fit or do I have to buy another test pipe? first pic is the headers second is the test pipe any help is appreciated

[AWDream]

it's easist to buy another test pipe so you're not creating a bottleneck in the exhaust with a smaller testpipe

[LP1029]

Ok is there any specific text pipe i should get
Because i bought a whole exhaust off of ebay
And the whole exhaust is 3 inches i just wanna make
Sure the test pipe fits both the headers and the rest of the
Exhaust!