Unstable hit the key phrase... "Flying the Tail".

That's exactly what you need to do with a taildragger. Once the tailwheel is off the ground, you have to fly the tail until airborne. And BTW, don't release the rudder as soon as the mains are off the ground, if you do, you'll notice a quick (but slight) fish-tail to the left. Ease off the rudder gently as the speed increases.