It's a tricky and clever-sounding statement, a half-joke because it's phrased in a surprising way that stops you and makes you think.
The meaning is: "I planned to reach a destination. I've come part of the way. I'm not going to stop here. I'm determined to go on and reach my destination."
These would be straightforward statements:
"I didn't come this far to turn back now."
"I didn't come this far just to see the mountain, I came here to climb it and I'm going to."
The tricky statement is correct, but some implied words have been left out. A plainer statement would be:
"I didn't come this far in order to only get this far." That is to say, "My goal was not merely to get this far."
Without more context, I can't guess why the speaker used this phrase.
OK, I just Googled. It seems to be come kind of catchphrase that's becoming popular. Lots of celebrities seem to be using it. It's slightly clever or joking precisely because the second phrase is unexpected, and the repetition makes you stop and think for an instant. Obviously, people hear it, think it's cool, and then use it themselves.