Was it ever right?
If it worked right once and it doesn't now, it's probably not the derailleur. That leaves the shift cable and the shifter.
Try disconnecting the cable from your front derailleur. Hold the cable taut with your fingers and try cycling the shifter. If you can feel cable movement, in and out as you shift, the cable and housing are probably OK.
If that's the case, be sure to first cycle your shifter into the smallest gear position, pull the cable taut with a needlenose pliers, and reattach it to your derailleur.