Where you're wrong^ is that God didn't create us that way. It's our own free will and choice. We were born with sin. It's in our human nature but it's our choice to either rebuke and turn away from that sin or act on that sinful thought. Like it clearly states more than 1 time in the Bible about God stating homosexuality being an abomination. Yes, God loves each and every one of us, but hates our sin.
People will always try to defend the homosexual lifestyle by saying we are to love everyone. Which is true, but Jesus said "if you love me you will keep my commandments"...iti s also clear that Jesus said mariage was between ONE man and ONE woman, and Paul confirmed through the Holy Spirit that homosexuals will not enter the kingdom of Heaven. People also do not understand that attraction is desires of the flesh which is against the spirit. God does not approve of fleshly desires.
Yet, people will continue to twist scripture to make themselves feel better foolishly thinking it changes Gods word.
Anyway...in saying all that you do need to calm down a little. You're 16. You're not a little girl and not a full grown woman yet either. You are at THAT AGE where many things are confusing. Sexuality is more talked about in public and homosexuality is more accepted by society. I can see why you are having certain thoughts. While they aren't good thoughts you aren't the onle one that has thought this way.
It would be a good idea to stop looking at videos of gay families, and you may need to stop associating with your bi sexual friend if you feel she could be part of the problem. Sometimes we dismiss thoughts and put them in the back of our minds and then one day they just kinda pop up front and you wonder where it came from. That is sort of what the subconscious does.
The best way to avoid it is to pray for guidance and deliverance and to stop associating with anyone or anything dealing with bisexuality.
You are still a normal girl though. Don't fret too much, and at least be glad you recognize the issue and you are wanting help for it. God knows this, and is happy you feel the conviction.
Hang in there. Teenage years suck, but you will survive and before you know it you wont worry about this stuff anymore(no I am not talking down to you, I am sorta jealous I am not your age anymore)