So my partner and i had unprotected sex where i pulled out, ejaculated, then put back in. we immediately stopped she then used spermicide, then took a plan b the following day. she was at the beginning of fertilization but not ovulating?

I guess you are asking what are the chances of pregnancy. Plan B is up to 89% effective at preventing pregnancy if taken within 72 hours (3 days) of unprotected sex. It’s very safe, well-tolerated, and won’t affect future fertility. Plan B isn’t effective during or after ovulation. ref: https://www.goodrx.com/plan-b/how-effective-is-plan-b

The chances are close to 0 but not 0 as all these can have a failure rate.