My period cycles are kind of random, but always longer, more like 35 days in length. Does that make a dif in determining due date?

I just went off the app, I believed I ovulated on may 11. I conceived a baby that month.

I have just been going off of date of last period for due date, which would make me 8 w 6 d. But is that what I should do even with longer cycles?

I will say I tested at 9 dpo (what I believed to be 9 dpo), and got a negative test. 10 dpo I got positive tests. I started feeling pregnant at 8 dpo.

My hcg levels are in range but on the low side which kind of concerns me since I’ve been spotting too.

Do you think it’s possible I’m less than 8 w 6 d? I don’t have an ultrasound for a few more weeks to better confirm due date