Are you installing by yourself with a jack lift?
And by not lining up correctly do you mean that you got the pipes alight but the screw holes dont?
If not then try getting someone to help you, theres a flex joint on the downpipe correct? That should allow you to bend taht pipe a bit. So just push the pipe back towards the cat. and align the holes with the screws.
If im talking nonsense can you post a pic so I can see what your problem is?
And by not lining up correctly do you mean that you got the pipes alight but the screw holes dont?
If not then try getting someone to help you, theres a flex joint on the downpipe correct? That should allow you to bend taht pipe a bit. So just push the pipe back towards the cat. and align the holes with the screws.
If im talking nonsense can you post a pic so I can see what your problem is?