Had sex on the end of my period but he did not cum. He may have pre cum though. I took the ellaone pill 3days after and I'm worried that I am pregnant?

Maybe/not. Pregnancy has been documented from exposure on any day of a woman's cycle including during menses.Precum has enough sperm to do the job & the pills work better when taken closer to the time of exposure. What you describe is a lower risk scenario than some, but some risk of pregnancy remains.