Aircraft Technician reported loading incorrect amount of fuel onboard resulting in engine flame out inflight and a diversion to another airport.

Narrative

Aircraft came in with a requirement to accomplish a known fuel quantity. Due to the fact that #2 fuel tank quantity was on MEL. Upon aircraft arrival; I walked into the cockpit to commence the procedure. This is my very first time performing this procedure with the new [company] work card # XXXXXXX-XX-XX which became effective [recently]. Flight required 78.5; Block in fuel was 24.9 calculated by the crew and noted in Maintenance Release YY-YY/YYYY. I incorrectly miscalculated the fuel and added a total 6939 gls/45.1 lbs using a density of 6.5. First error was the number two tank block in fuel quantity; I noted 9.1 on the fuel service form and it was actually 6.7. Total fuel added was 70.0 Which was short of the 78.5 required. The #2 eng flamed out and diverted to ZZZ1. A/C landed without incident [Maintenance Release] AA-AA/AAAA Fuel in number #2 tank was determined to be at zero qty upon arrival into ZZZ1. thus the #2 engine flamed out.The following factors contributed; I was overwhelmed by the new fueling job card #XXXXXXX-XX-XX which was my very first time using it; as it became effective [recently]. Besides a maintenance alert notice; no type of training was provided in understanding and or using the work card. I would suggest training in using this new job card. Two fuel trucks were dispatched which added to the work load. The weather at the time was very poor; heavy rains and winds. The outbound flight crew was also onboard the a/c which was a distraction. In dealing with the distractions and trying to meet the departure time; I made the unintentional mistake of under fueling the aircraft. I suggest that the flight crew is not allowed in the flight deck until this procedure is completed.