Tailgraggers require a different approach to takeoffs.

You need to hold full up elevator WHILE TAXING to keep the tailwheel on the ground.

For take off, hold A LITTLE up elevator while doing your takeoff run, you will also need to BE READY to feed in rudder. As the plane gets up to speed, ease off on the elevator. At this point 2 things happen: 1. The plane is going to want to go to the left and 2. the tailwheel no longer controls the steering, it is the rudder. SO, as you accelerate on your takeoff run you will be holding A LITTLE up elevator AND you will be ready on the rudder, as you are accellerating toward takeoff speed (at about 1/3 - 1/2 of the takeoff speed) START EASING OFF on the elevator.

Watch the plane CAREFULLY. AS SOON AS THE TAIL BEGINS TO LIFT, start feeding in RIGHT rudder to keep the plane running in a straight line. At this point, the plane should be taxing at a high rate of speed and be up on the main gear. Now feed in a LITTLE up elevator and BE READY TO EASE OFF ON THE RUDDER. DO NOT RELEASE THE RUDDER, just gradually ease off AS THE PLANE LIFTS FROM THE GROUND. Once the main gear comes off the ground, the amount of pulling to the left will be reduced.

I realize this sounds complicated, but it isn't. All it takes is some practice. If you have a GOOD sim, such as RealFlight G2, that has/allows ground handling, practice on that.