Too short of an exposure most likely. It would be good if you could measure your pinhole diameter so you can work out the f-stop you should factor your exposures from. I have no idea what a #14 pin measures, maybe you can find that out somewhere. I use my enlarger to measure the pinhole by projecting it and measureing the circle then calcuating using the magnification factor. If I recall from usefilm correctly you don't have an enlarger yet, so you won't be able to do it that way. If yo have a slide projector you might be able to use that. If you can, there's a nifty exposure calculator at

I use Agfa RC usually and it has an effective speed of 4-6. I actually also stick a Grade 00 filter across the pinhole to lower the contrast a little, but that slows the speed in half again, not that it really matters.

If you can't work out the size of your pinhole accurately, I suggest doing tests shots, using a smaller piece of paper since there's no point wasting a whole piece, doubling the time until you get something reasonable, then fine tune They don't need to be too 'black' as I think you find they hold detail when being lighter than you think they should be. Contact print them to see how they really behave.