Question about a "cat back", Mine was done wrong! read Options

[mgnt232]

So about a year ago I bought a magnaflow res and muffler. And I brought them to a local shop to get it put on expecting to be done right. But they used the same 1.75" piping that was there.... the magnaflow is all 2.25"
Now i know that a catback is not too much of a performance upgrade, but wouldnt it work better with 2.25" piping from the cat back?
They said they dont bend pipe there (which they dont) but I was at the auto store today and saw some flexible piping, is this stuff junk or would it work? or doesn anyone know what I can do?
I can put pics up of what they did... stock exhaust - manifold - cat - magnaflow res - stock pipe - magnaflow muffler
I know it sounds dumb lol... im not like retarded lol I just dont know anything about "custom work". i went to votech in HS and I know a bit...just not about "custom work".. like i put in my own engine, just dont know how to go about this work