Getting the wood stain out isn't easy. One thing you can try is to apply the stain again. Only this time thin the stain a little, 25%. This will darken the window frame a little more but it could help.

Something else you can try is to wipe the dark areas with a clean rag with some paint thinner. This could redistribute some of the pigments, reducing the blotchy look. I'm assuming you are using an oil based wiping stain, this is the easiest to use.

I didn't use a pre stain wood conditioner. My beautiful pine window frame is a blotchy mess. How do I undo my error and get the stain out and start over

You will have to strip and sand in order to get to a clean un-stained surface again. Try hand sanding with a sanding sponge an area first and see how it goes.