First, agree with DoctaDave, too thick rubber, not winding anywhere NEAR hard enough. You should be using rubber of about 3/32 thick and winding 1000 to 1500 turns on these motors. Rubber motors have a non-linear relation between turns and torque. At low turns like that you disproportionately low on torque, and you need torque to climb.
I will disagree on his comments about weight. He's right, you can get a heavy plane to fly. BUT, its a LOT easier to get a light plane to fly. Make sure your plane weighs close to 7 gm.
Adjustments/trim. You really should start close to what's recommended, you plane is more likely to fly close to desired and you will only need to tweak it to optimize trim. Then you can focus on matching the prop and rubber, your real task.
General comment to help understand why so many adjustments related to turn. These planes fly at a variety of speeds and with a varying range of motor torque. The various things done to help turn work differently at different speeds, some more effective at high speed, some more at low speed. You need ALL of these adjustments in place to maintain a consistent turn radius. Everytime before you launch you need to check that these settings are OK.
- Your wing should be square to the motor stick, small amounts won't hurt much, but I mean small. If you can see significant skew, cut off the offending wing post and fix it.
- Make sure the left wing tip is at a higher angle of attack than the right (washin). It doesn't take much, but without it you will struggle to climb even when you have enough winds. This generally requires you to crack the front spar and reglue it so the left side kicks up about 1/8 of an inch. Once you start flying you will adjust this so the plane flys with only a SLIGHT left bank to level.
- Center of gravity is important, as a starting point for these planes it should be near the rear wing post. Adjust wing and stab angle of attack to fly consistently with the cg to the rear like that. Yes it is different than man rated planes and RC planes. But it really needs to be there so you horizontal stab helps with lift.
- I once designed a plane for WS teams that had and adjustable tail. For an experienced flyer, it worked OK, but was unnecessary. For new teams it just turned out to be a way to fail, causing inconsistent results making it harder to interpret and trim. Don't use tape or a rubber band to hold tail boom position, you are asking for problems. Glue that tail boom to the motor stick with the recommended offset. Its easy enough to change small amounts by warping, larger by cracking and regluing.
- Make sure the horizontal stab is perpendicular to the tail boom and tilted with the left side high (about 3/8 to 1/2 inch).
- Don't trim turn with the vertical stab or a rudder tab. Its TOO powerful and TOO draggy. Make it parallel to the tail boom and leave it alone.
- Most of your turn trimming will be done by adjustments to the tail boom. Angle from motor stick and stab tilt.
As I write this, I'm reminded about something I learned so long ago that I take it for granted. We all build carefully to make sure that the plane is as accurate as possible. However, its impossible (or at least unlikely) that it is built perfectly. More experienced builders will be closer to right more often, but still not perfect. As a result, you HAVE to learn to be comfortable with sometimes major surgery when trimming a new plane. It is NORMAL to cut a component half through, crack it and reglue to add a kink, or adjust a tilt. Become comfortable with this fact.