I think from your question you are looking for someone to make a decision for you that only you - and your coach - can make.
Your coach certainly knows more about you and your skills than anyone here. It's not just about your speed or your ball skills, but about your ability to think on your feet, too. It's also about approaching any position you play with the right attitude. Try out the back row and see what happens. Have faith in your coach and what he sees in you. And as others have said, you're young and still growing and you may try several positions before you find the perfect fit. You never know until you try.
Also, ask yourself why you're skeptical about the back row. Is it because you dreamed of something different, or because you question your skill? If it is the former, then learning to appreciate the position and its importance to the team and the game can help you to have the right attitude, and having the right attitude about the role you play in the team is half the battle. And if it is the latter and you're not confident in your ability as a back rower, give it a try and give it your all, and perhaps you'll find you're a natural in the position. And if not, then at least you know and you can move on to something else until you find what works best for you.
das