Possible ovulation

So I got on birth control recently because we have an 8 month old and are wanting to wait about a year before trying again. On September 11th I had very light spotting, the day before my estimated ovulation day. My husband’s bday was the 12th and we had sex. I’m curious if the spotting was caused by ovulation and if there’s a good chance I could get pregnant from this? We would be happy it just wasn’t the plan haha 🤣 I thought about getting a plan b but my husband said if it happens it happens.. plus that’s $50