It looks a goregous colour I must say. Quite often hair that has been coloured before seems to take henna much stronger than virgin hair. So that could have an affect. Also I thought henna glosses should only be left on for an hour or so, maybe even less. Plus I know a lot of people here saying freezing it helps dye release, and I guess if you only want to do a gloss, then don't bother preparing the henna with dye release in mind, so don't freeze it or leave it cooking for hours before using it.
Plus, are you absolutely sure the henna you used didn't have any extra added ingredients given it's described as "bright red"?
Whenever I've mixed henna, it never looks red, always greenish brownish cow pat type stuff!
As for not using a metal bowl, nearly all henna instructions I've come across say not use metal bowls and spoons etc. I always stick to a glass bowl and wooden spoon to mix it, so the mixture never comes into contact with metal.
As for lightening it, perhaps try honey lightening? Also I know sun in has been used for lightening henna, there's a thread on here somewhere.
Good luck
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