Best way to fill gap between wooden bath panel and wall

[DeusXM]

Ok, because I am an idiot and bad at measuring, I have a gap between my new end bath panel and the wall.

It's a 700mm panel but apparently a 730mm bath - didn't realise that was a thing and when I originally measured, I stupidly thought 'close enough'. The supplier doesn't do 730mm panels and there are some background domestic issues which mean I would want to send them back again.

So, how do I fill the gap?

The panels are made of sealed MDF. As this is in a non-visible corner, this doesn't need to be superperfect. As you might see in the photo, I have a square shaped piece of spare plinth left over, but for it to fill the gap, I'd need to cut it into slices so there'd be a 'ladder' effect.

Would a bit of melamine cut to size do the job? It's only a dinky job so was thinking get a bit of board cut, get a tester point of their paint and primer colour matched to the plinth, paint it, glue it in with wood glue and then seal off the edges. Would that work?

 

[foxhole]

Off cut of Upvc trim would make simple infill.

 

[Tigercubrider]

Is the mdf panel prepainted?
You could cut a strip of mdf and paint it the same colour, sticking it to the wall,
or ( more work) join it to the panel.
Joining it to the panel with something like gorilla glue and using filler to fill the seam would work but may depend on what's behind the panel. If you can have a second strip of mdf that fits behind the solid bit of the panel first, and the second is stuck to that as well, it would be strong.

Colour to suit

 

[foxhole]

Or infill with recessed timber and fit wall tile flush.