Hey there Bexjohnson :D
Picky eaters can be difficult, but you just have to be consistant. If possible, try crushing a piece of fresh garlic into a glass bowl or cup and add the tiniest bit of water before microwaving for a while. This'll make a really pungent garlic juice which you can soak your pellets in before feeding. Make sure the pellets are soaked all the way through, then offer two or three. The garlic stimulates betta appetites and the strong odor is difficult for them to resist. If this doesn't work, don't worry. Try tapping the water near the food to let your betta know that there is something over there to be investigated and perhaps eaten. If that doesn't work, ust keep offering food twice a day, and he or she will get the hint.
As for whether or not he or she is a guy or girl, Alanthebro was only partially correct. Guys and girls flare, but they flare differently. When males flare, they turn sideways and flare so that they look bigger and more threatening. They also have beards. Females have tiny beards, but they flare facing the mirror.
Along with that, check the ventral fin length. The ventral fins are the two fins which hang down from their belly right below their head. Males have long ones that tend to be thick and full. Females have short little stubs. :)