What did I do wrong?

here are some photos

I would give it another coat.
I don't think you have done anything wrong, that is the type of result you get with a weakly pigmented dye like Lavender, especially on a darker base

Best to leave it on for longer or is 4-6 hours enough? Which colour would be say one up from lavender that would show more but don't want a proper Cadbury purple iykwim? Am I best putting more on tonight on dry hair wrap it up in a bun and leave it until I get back from work at 9 so it will have had nearly 12 hours or won't it make much difference

This dye needs a platinum blonde base.

Which colour would work then? But don't want a purple that's bright , I've used pimple purple before and that was too bright . I like the dull purple but don't want to go dark again as I've taken ages getting lighter

Also one last thing, does the direction dye ruin your hair at all? The bottom has gone really bad condition it's like breaking off ?

You can dilute a darker purple with conditioner.
I don't think leaving lavender on for longer will make a huge difference, pastels often need two coats though

i think your hair is too dark for the dye. try what wicked pixie suggested and dilute a darker purple. you can look in the gallery for a pink based purple.

I redid it last night and left it over night and definetly looks better this morning still a bit patchy on the side where the hair was blonder which is strange but much happier. Thanks for all the advice 👍🏻
Which shampoo is best to keep the colour I normally use faith in nature or treseme undo ? Don't have a Sally's local

I am not familiar with either of those but to keep your color nice you want to use sulphate-free shampoo (SLS) and you can add some dye to your conditioner to top it up.

I would really highly recommend co washing (washing with just conditioner) if you want to maintain any colour, but especially pale colours. It makes such a huge difference even compared to sulphate free shampoo.

Thanks for the advice . So I don't use any shampoo just wet hair and use conditioner ? Or do I add some lavender to the conditioner and wash as normal or do I need to leave conditioner/colour on for amount of time?

Use conditioner just like a shampoo. You'll want a thin cheap one for the wash and a richer one for the usual conditioning.

No point in adding dye as you won't be losing much dye each time, the cuticle won't be lifted and you won't be fully washing off barriers to the dye. It's still washing well though! It can take a few washes to get used to it though. You might have slightly greasy hair at first.

I used just conditioner but couldn't handle the grease 🙈 So used my natural shampoo and loads have come out ! It's more a silvery purple now 😔

No, Directions is actually conditioning, it is like coloured conditioner so it doesn't damage the hair at all.
Any damage is from the bleach and the age of the hair, if your hair is 18 inches long your ends are at least 3 years old so they have been through a lot.