Hi and welcome to the SI101 Board and its Forums.
Kids in your age bracket are exploring as you stated. Many questions and concerns crop up such as "am I gay/lesbian", Bi-, straight. Some people know from an early age, some late(r) in life, others sometime during their journey thru life. If you are curious then just be open minded and discover what develops for you over the next few years. You do not have to be anything right now. Let your raging hormones settle down, first. This will take a few more years. Once they do then you will have clearer knowledge about how you are "wired".
Please read this article:
Male / Female Sexual Behavior--If I like certain things does this mean I'm Gay?
Fantasies are just that. They can be about any subject or script. Do not be concerned if some are even outlandish or bizzare. As long as you do not act on them, any are fair game.
If a hot girl or scenario turns you on, that's OK.
If a hot guy or scenario turns you on, this too is OK.
If group sex scripts turn you on, have fun imagining.
Fantasies are designed to help turn us on, so let them and do not be too concerned about the scripting.