It’s common practise to keep the low frequencies centred. I always go by the rule of thumb that the higher the frequency, the harder it can be panned. For example, bass should be kept centred, mids can be mildly panned (with the exception of vocals or lead instruments), and the highs can be hard panned (100% left or right) to give a crisp and spatial mix.
Make sure there is balance though, as there is nothing more annoying and distracting than an off-balance mix. With every pan left, make sure something is there on the right to balance it out, and vice versa.
I reckon once the bass is dealt with and the saxophone is modified / replaced, you could hand it in and it has a good chance of being accepted.
Keep working on it and make sure you post the new track before resubmitting so I can have a listen 