Probably have to re-dye it.
Yep, it takes a lot of dye to get a really strong good red. And you have to really mix it well too. I always have to strain my red dye through a coffee filter because it doesn't always want to dissolve.

That is part of the reason why red fabric bleeds so much. It takes sooo much dye to get a good strong color that there is often lots of residual dye left in the fabric and it will eventually work its way out again. You also need to add a lot of salt to help it to set. I rarely vat dye red because it takes sooooo much dye.