I can tell you that if it was the needles that was responsible for the reduced flight time, rookie or not, pretty sure you would have noticed the engine running pretty bad, if at all. The fact it developed enough power to give you the confidence to even try a take off alone says quite a bit.

Nothing is impossible, but my focus when looking for this problem, would be elsewhere first.

Can you hint were I should look ?

The vent line location is the only thing that comes to mind. Or maybe a bad leak in the fill line if you are using a 3 line tank plumbing system. If that checks out, I'd give it another try, checking/double checking everything every step of the way, to see if you can reproduce what you believed happened last time out.

Eg: when you fill the tank, confirm it IS actually full. If you feel it's necessary to tune further, refill the tank when you're done tuning, prior to flying. If you don't want to risk another dead stick landing, or you want to minimize the chances of one, maybe just fly for 3-4 minutes, then land and check your fuel level to see how you are doing. Best of luck!

I did check the tank whilst filling it and everything is OK. The tank filled all the way up and there were no leaks anywhere. I did not however had the engine running. Just filled the tank up. Due to the way the plane is standing there was only a small gap in the top corner of the tank without fuel. The problem is elsewhere.

Whatever changes will be done to the system I will definitely fly short times and check the fuel level after each flight.