Have you got the derailleur on the hanger properly? It should be off the back of it, not down, chain should be the right length but it's probably not affecting it, and yeah, the B screw will need setting properly.
Cheers, all that looks fine to me so my working hypothesis is I'm misunderstanding the B screw and need to try turning it the opposite way
@Cupcakes started
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Have you got the derailleur on the hanger properly? It should be off the back of it, not down, chain should be the right length but it's probably not affecting it, and yeah, the B screw will need setting properly.