Had sex 3 days after period ended and condom broke. no ejaculation but probably pre ejaculation.took plan b within the hour. pregnancy chances?

Not likely: Not likely a fertile time of the month. Not likely that sperm got in. Not likely that Plan B failed. Not likely that you are pregnant. But best to use a second method of birth control in the future if you really want to be safe going forward. And do a pregnancy test if your period hasn't come by a week after it is due.

Unless you had other: Episodes of unprotected sex, the likelihood of pregnancy in this case is very low. Probably less than 1% risk. That said, you aren't protected against sexually transmitted infection. You may want to see your family physician or gyn to be tested for STIs in a week or so, especially if you have unusually pain, cramping, pain with urination or unusual discharge. Wishing you well!