Kinda hard to tell what went wrong...
We don't know the developing temperature, development time, type of agitation, shutter speed of the camera, aperture, lighting conditions...
That's not including the fact that the concentrations used in the developer can vary quite a bit from batch to batch...
Maybe you could fix it by scanning... depending on how dark it is...
I don't know if using a reducer on the film would work with a stained negative...
But on average, caffeinol processed film should print fairly fine... they just need more time in the enlarger.
