You are rounding. To help combat that you can raise the arm pull line height of the throw to shoulder level. That can help in avoiding throwing high. In fact some have a problem of throwing down 30' in front of them initially.
Your throw is all arm and depending on your health it may be the only choice. If your ankles, knees, hips and back can take it safely reaching back more will move your distance to a whole new level. I don't recommend reaching back fully at first for several reasons. One is coordination. Most can't maintain balance, timing and muscle control to accelerate if they go to a full reach back. Because disc golf is more an accuracy sport than a distance sport control needs to be emphasized. Distance comes with it in time. In order to get controllable distance one can't take eye sight off of a target too long. Or at all.
That means that the first step shouldn't have the foot pointing more than 90 degrees left of the target and the x step more than about 120 degrees and the plant step more than 90. When you test the hips left of neutral in the arm reach back and the shoulders even more you increase the arm pull length about a quarter and that transforms the power you'll generate. Meaning i wouldn't wonder if you wouldn't throw past 250' soon as long as you throw low with drivers. Not face height but say under 12' height.
In the throw you should also twist and turn the hips and the shoulders right of neutral before straightening the elbow.
Another nose down tips is wrestling the wrist down in the elbow chop. If you start with you arm super loose you can allow the wrist to hang down as far as it can go. It won't stay there unless you use muscle power to keep it down late in the throw. You had the disc aligned traditionally in the seam of the hand. You can also raise the rear of the disc in the grip up to the innermost joint of the thumb. Most won't go that high because it can tense up the forearm muscles slowing the arm down. It depends on hand and finger size, flexibility and muscle power if the muscles get tense. Stretching, working those muscles with weights and grippers plus throwing a lot in field practice will loosen up the muscles eventually.
The most important thing now is to not stay flat footed -it will screw up your form and worse your health.
Flat shots need running on the center line of the tee and planting each step on the center line. Anhyzer needs running from rear right to front left with the plant step hitting the ground to the left of the line you're running on. Hyzer is the mirror of that.