"나는 미국에서 왔어."
Translation:I am from America.
I'm not sure if a native will understand it the way you are meaning it (I'm not native), but as a literal translation, it seems correct too, indeed.
However, note that this structure seems to be used most often as an answer to this question:
어디에서 왔어요? Where are you from? (like in, which country are you from?)
Again, it is completely contextual. It should still be accepted in my opinion
That is literally what it means; maybe in real life you'd have to give some context. like when you left America, to make it clear you were just talking about one journey.
That makes it sound like you're on a trip around the world, you've recently arrived in whatever country you're now in, and before that you in America, whether that's your home or not.
For instance: I'm from Australia and I'm currently in Korea. I came from Japan. The ferry to Busan was very relaxing.