It's too small for me to tell yet. It looks "girlie" so far but it's top & bottom fins can grow longer as it grows & matures. Your middle pic looks like the anal (bottom) fin is "almost" boyish long but not in the other 2, could be the pic angle. The dorsal (top) fin is still rounded in a "girlie" way...& that's why I vote for female...for now ...How that for wishy washy?
Congrats on buying a younger fish, you'll likely have it live much longer than getting a big, possibly old betta. I always prefer to buy younger fish. Some female bettas are "almost" as pretty as males, some of that depends on the strain.
I try to get young fish when I buy them. I named him Ace on the assumption it said baby boy on it. He's grown since I got him in July he was according to a growth betta chart online about 6 weeks maybe when I got him maybe 5.