Look thats far too early to tell in the picture and if you flower enough plants you will see this exact same thing on both male and female. If it were a real preflower and not some pre flower hormonal defect it would grow quickly everyday accompanied by many others and after a short wait you wont need to be asking what sex as it will become perfectly clear.
Many growers seem to expect plants to show sex after a few weeks veg - it dosent always work like that and you will need to flip to 12/12 to get preflowers as a general rule.
Just wait things out - no misinformation just good advice that will make you much better at sexing your plants.
Peeps should be able to google up a few threads with weird preflowers or stuff that looks like balls on a female fem seed plant that then goes onto become 100% female just to see the stuff i speak off.