Of course you should ask. Communication with your coaches is a very important part of soccer, or any sport for that matter. Whenever you talk to your coaches, you need to be respectful and show them that you are really listening to what they have to say.
Things to say:
1. Ask them for the opportunity to play on the other field so you can show them what you are capable of.
2. Ask them what you could do to improve if they are not satisfied with your play, then work on those things.
No matter what, make sure you aren't just psyching yourself out and continue to do your best. If you continue to work hard and have a good attitude, things will work out one way or another.
I was in the same situation once. I said ' Im easily better than most of the people here. Put me on the team for one full match and I'll prove myself. If you don't Im leaving the team'. And it worked i played in most matches since
Start going to College or Professional football / soccer camps where the coaches and scouts evaluate you and give sound advise about how good you are and where you can improve.
Sometimes just being the fastest person on the team or being the fastest dribbler is all a coach looks at.
Yes, you should ask. If he is not noticing you as a starter or valuable player, then talk to him and ask for a chance as its the only way for you to get a game.