Stain Lightening

Not knowing the wood type I will try to help, the best time to lighten is when stain is wet, within 30 minutes with paint thinner for oil base stain, once it cures you likely will smear it. To see its color now get it wet with thinner and you will see how really much darker it is. If its pine I hope you used a shellac base pre stain or it will likely have gone into the grains unevenly. If its cured use paint remover and some stain will remain and it might be your color when wet- wetted, if not pre stain if pine and restain.