Plants won't stretch.

The stretch will come in time my friend. Sit tight and good luck with your grow :)

You are only going to get so much additional stretch out of a ruderalis hybrid, but introducing (or increasing the amount of) far-red light (IR) in veg or during early flower will stretch it:   “We get asked a lot about how these photobiological ratios apply to cannabis. The good news is that my laboratory has a state license to   study cannabis. So we've applied these ratios to predict cannabis growth, and they have the same value in cannabis as they do in all other   crop plants. Adding far-red is both good and bad and that's why the sensors are so important. You want to add the right amount at the right   time to get full advantage of it. More far-red can make cannabis plants taller. That’s usually bad. But it also helps expand leaves. That's   good, and there's evidence it can help with slightly earlier flowering, which is another benefit. So this is emerging research.”

      Dr. Bruce Bugbee. “Predicting Stem Elongation and Leaf Expansion: Percent far-red is a better predictor than PPE”, YouTube,   www.youtube.com/watch           “In controlled environments, Bugbee suggests applying far-red photons early in the lifecycle to help close the canopy and capture   all available photons, then minimizing far-red during stem elongation early in flowering to keep plants short. With that phase finished,   Bugbee says, the last four weeks before harvest open the door to apply far-red photons again.”    
  Bruce Bugbee, “Far-Red Lighting and the Phytochromes”, Maximum Yield, 
  www.maximumyield.com/far-red-lighting-and-the-phytochromes/2/17443   I will be covering up the IR diodes on my light during early flower this grow. Bugbee's entire video on far-red (Far-red: The Forgotten Photons) is an easier watch than the nerdy one from the above quote.      Dr. Bruce Bugbee. "Far-red: The Forgotten Photons, Dr. Bruce Bugbee", YouTube   www.youtube.com/watch

It’s the ruderalis more than anything if we’re talking about genetics - which it is more than likely

You may have your light intensity up too high.

io sono un cultore delle piante corte e ciccione quindi adoro gli internodi corti... dopo questo preambolo veniamo alla spiegazione intanto sono appena in prefioritura quini almeno un altra settimana sara' in vegetativa l'allungamento avverra' un po' in ritardo come ha fatto a me.. quindi aspettati l'allungamento tra 2 settimane piu o meno..

Unfortunately there's nothing you can do at this point. Next time I recommend planting in a bigger pot a less training/ less stress. You'll end up with a bigger auto. Or just go with photoperiod plants and that way you can control they're veg and bloom cycles so if something were to go wrong, you can correct it and not have to just deal with it like with auto flower plants. Hope this helps