Ttc baby #2

I got pregnant when I was 21 the first time my boyfriend and I didn’t use a condom. It took one time. This is my 2nd month trying to conceive and I used opks to track my ovulation. Glow said I would ovulate on Wednesday the 21st (yesterday) but when I got my positive opk I logged it into the glow app and it changed my ovulation to Monday the 19th. My boyfriend and I only had sex Sunday night the 18th and I’m hoping it only takes one time this cycle. Ladies have any of you only had sex one time and you conceived? I’m needing some hope right now.