I concur with the comment about securing the fuel tank better. I've had them slide forward and backward even when secured much better than yours appears to be.

One trick I've used is to secure a strip of adhesive backed Velcro onto the tank and then use the Velcro straps across the Velcro on the tank. This helps remedy the dilemma between having to get the straps so tight they break something vs. loose enough for the tank to slide. I would definitely consider a better securing method before flying it.

In the attached photo the tank continually would slide forward even with the Velcro strip on the tank until I added the green Velcro anchoring strip.

Keith B