Pilot of a Beechcraft Premier jet reported loss of directional control after takeoff. After regaining control and returning to the airport; a fuel imbalance of about 1300 pounds between the main fuel tanks was discovered.

Narrative

Upon arrival to the aircraft I was told the aircraft was topped off with fuel. I even asked twice if they indeed topped it off with a yes answer each time. I hooked up the battery; checked the oil; went into the cockpit and turned on the battery master to get the air conditioning running and noticed a significant indicated fuel imbalance; not being too concerned at the time because the Premier has a known issue with faulty gauges. I went out to the fuel tanks and verified that there was fuel noticeable in the fuel tanks. I did see fuel up to the neck in both tanks and in the cup. I continued with preflight preparations and decided to look one more time because I felt another look was warranted because of the significant indicated imbalance issue [and] this time the owner was present for the inspection. I removed the suspect fuel cap (left side) and saw fuel in the cup and up to the neck. I thought nothing more of the issue because I have personally seen issues with the premier fuel gauges in the past and I did see fuel up to the neck. I didn't feel pushing the flapper inside the tank was necessary because a long time FBO employee assured me it was topped off and being dressed to fly I didn't feel the necessity to put my hand in jet fuel because there was fuel present on both the wing and the ground accepting it was indeed full. I continued with the flight accepting it was a faulty gauge. I got cleared for takeoff from Runway XXR and immediately after takeoff the aircraft was uncontrollable using normal control inputs. Using differential thrust and speed I was barely able to keep the aircraft flying. I requested a return to the field not knowing at the time why the aircraft was rolling to the right so violently. I successfully managed to get the aircraft back to Runway XXR using all means necessary without incident. I suspected a floating spoiler or flap asymmetry. Upon further investigation and after pushing the left hand fuel flap down I suspected a fuel problem. I called the fuel truck back over and had them top off the aircraft keeping note of how much went in each tank. 11 gallons went into the right and 189 gallons into the left. I had almost 1300lbs fuel imbalance. The cause of the incident was a SIGNIFICANT fuel imbalance caused by the fuelers. The take away from all this is push the flap down inside the fuel tank and make sure it wasn't a false fill. This incident could have ended a lot worse. The Tower was a huge asset in this event. After talking with the fueler I was told he fueled the left hand fuel tank and fuel was spilled running over the wing and onto the ground leading the fueler to believe the tank was indeed full. IT WAS NOT! great care and patience are needed when fueling a Premier jet.