I'm guessing you are in the UK. Is there no way you can plant it in the ground? That would be the best solution. If you can't I would repot it in John Innes no.3, not that multi purpose compost.

Does the pot have holes in the bottom? If so, after repotting I would give it an absolute soaking - and I mean absolutely sopping. Then leave it for a week and do it again. If there are no holes you need to put some in. You will also need to repot into a bigger container after 2 or so years. Fruit Trees in Containers

transplant shock ..

poor media for a tree ...

and over watering ...

it would have been better if you had potted it up.. BEFORE it leafed out ... then the leaves wouldnt have looked like this.. since they wouldnt have been there ...

it is also best to put a new transplant in full shade until the roots start working ...

i would not water it again ... until your finger.. inserted 3 inches.. indicates the media is drying ...

if i were to have done this.. i would have used up to half wood chips in that media you used ... trees like a sip of water.. then near total draining.. and near drying before another sip ...

your muck will keep it too wet in the long run .. unless you are very keen on making sure it doesnt stay sopping wet ...

the problem with that all-purpose stuff.. is that annuals and perennials... like very spongy wet media ... and i am sure that stuff is great for that ...

but not for trees ..

good luck

ken