Your first few sermons are always terrible, no matter who you are. If you think your first few sermons are great, you're probably self-deceived. If the folks in your home church think your first few sermons are great, it's probably because they love you and they're proud of you. If it's a good, supportive church there's as much objectivity there as a grandparent evaluating the "I Love You Grandma" artwork handed to them by the five year-old in their family.
So your first set of sermons, unless you're very atypical, are probably really, really bad.
The great thing about Christian ministry is that Jesus doesn't start all over again with his church every generation. He gives older men in ministry who shape, disciple, and direct younger men in ministry. This includes (although it's not limited to) critiquing your sermons.
Your sermons will be critiqued. You want them to be critiqued, and harshly.
Now you don't want them critiqued harshly by your congregations (and a critical attitude toward your pastor's preaching, church members, is not a fruit of the Spirit). But you want them critiqued, and you want them critiqued now.
Your sermons will be highly critiqued early on in your ministry, when you're still being shaped, or you'll just be left alone.
The great preachers you hear or that you read about in your church history books are not almost never those who were preaching great sermons from the very beginning of their ministries.
Great preachers are the ones who preach really bad sermons. The difference is that they preach really bad sermons when they're young, and are sharpened for life by critique.
Mediocre preachers are those who start off with sermons that are, eh, pretty good, but they're never critiqued and thus never grow.
So if you're early on in ministry and you preach a bad sermon, so what? You're in a train of previously bad preachers that extends from Moses to Aaron to Simon Peter to about every good gospel preacher you've ever heard with your own ears.
Your bad sermon says nothing about your future. If you've got folks in your life saying, "Hey, that was a really bad sermon," that does indicate something about your future, so praise God for it. It's probably a sign that God has something for you to say, for the rest of your life.