So long as you have plenty of overlap all around for the seal, it should be fine. Just make sure you hold the trap as central as possible while you tighten it up. It's like taps and tap holes, invariably the holes are far bigger than the tap stems.
I would advise checking the smoothness of the underside of the tray where the trap seals and sand flat if necessary. Also it might be prudent to use some silicon to aid with the sealing underneath. The last thing you want is a leaking shower base once it's all in and fixed