What to do if undergraduate research has stalled for a long time?
You say you have learnt a lot, so you need not feel guilty. You do not think your work is publication-worthy yourself, and you also are leaving for grad school - so the only solution is to move on.

Make a neat report explaining your work. Even if it is not publishable, you could include it in your resume as a "technical report." From the tone of your question, this seems to be the only way out.