I'm thankful you aren't accepting this position thoughtlessly or just because it's being offered to you. Being a church officer is a serious responsibility, and you shouldn't take it lightly.
You have touched on one reason why it might be best for you to decline at this time: your own lack of spiritual conviction and stability. After all, whatever you're being called to do is God's work - and even if it seems like it only requires ordinary skills, it still has a spiritual dimension to it.
For example, churches need leaders who can watch over their financial affairs. But this not only requires good business sense, but spiritual wisdom to be sure the money is spent the way God wants it to be spent. This kind of wisdom comes only from a life built on a foundation of prayer and God's Word. The Bible says church officers "must keep hold of the deep truths of the faith with a clear conscience" (1 Timothy 3:9).
Ask God to show you His will about this decision - and then obey it. The most important thing, however, is for you to become stronger in your faith. Make sure of your commitment to Christ, and then ask Him to help you begin to walk with Him every day through prayer, fellowship with others, and the study of His Word, the Bible.