Let me assure you that God does care about every detail of our lives, including the decision you've made about your job. He knows what's best for us, and He wants to guide us.
After all, if God didn't care about us, we wouldn't have any reason to pray, because we'd have no reason to expect an answer. But He does care about us, and that's why we can turn to Him in prayer and commit our problems and decisions into His hands, knowing that He hears us. The Bible says, "In everything, by prayer and petition, with thanksgiving, present your requests to God" (Philippians 4:6).
Why didn't God make clear to you which way you should go? Sometimes we're impatient, and instead of waiting on God for the answer, we rush ahead and act on our own. Or sometimes God does speak to us, but we don't hear Him because we've allowed other voices (including our own) to drown out His voice. And sometimes we expect Him to speak to us in only one way -- a strong emotion, for example, instead of God's quiet voice. The Bible says, "Be still, and know that I am God" (Psalm 46:10).
Don't, however, spend all your energy worrying about the past or wondering if you've made the wrong decision. Instead, thank God for His presence with you, and ask Him to help you do your new job with diligence and joy.