Hi Damian,
You've taken some lovely shots there. The C3 / C330 (and C220) range are great cameras and Mamiya-Sekor lenses are among the very best - but they are as cheap as they have ever been.
However, giving film to the likes of ASDA to process is okay if the end result isn't too important to you. I suppose it's a bit like buying the best quality hi-fi equipment with gold plated terminals and speaker plugs only to plug them into the crappiest £10 speakers available from a second hand store.
Not all processing labs are equal. Yet it doesn't cost massively more to have the processing work done by a good independent shop or even one of the bigger companies that advertise in camera magazines. Also, my guess is that the scans will be tiny and will have been done at "auto" settings. It's probably not even ASDA but some local franchisee.
I don't know where you live but, as you've used ASDA it will be in the UK. If you can find a Jessops (not my favourite store by any stretch of the imagination) I've heard good things about their processing. Otherwise, I'm sure there'll be a thread on here for a good (and good value) lab. It'd be a real shame for any more to be ruined by clumsy / careless work.