First of all, I know that no birth control is 100%.

Here is my situation: We used a condom. It DID NOT break. My partner did NOT finish/ejaculate at all and I know this for a fact. But I know pre-ejaculation is a thing.
My concern is that we accidentally used an oil based lube, and I know that can weaken latex.

What are the odds that I could become pregnant from this? Should I take Plan B to be safe?

My period is due in 10 days and I'm on a 30-31 day cycle, it's possible that I was ovulating