Give it some more time, especially with it being your only plant there is no risk. You can always start to germinate another seed in the meantime. I had a pre-flower in the last grow that looked female, then male, then suddenly back to female with pistils and ended up being a tiny bud of larf in the end. From when I first noticed the pre-flower it took 11 days until I was certain it was a female preflower.
Check it out here.
Can you get a clearer image of the pre-flower?