First, use sticky tape on the outside (so it can just be pulled off) to hold the buttons and the trigger with its little spring in their right places in the left side of the handle. You've got enough to worry about without them dropping out on you just at the wrong moment
The pics show that you've got all the bits in the right places. You start by positioning the right side of the handle tight against the internal white rod AND THEN WHEN IT'S RIGHT NOT LETTING IT MOVE.
Your 'little black band' is the twist return spring. In order to locate the right handle side you have pull the ends of the spring apart in opposite directions (so they are under tension) see 1 in the pic and then locate the two ends either side of the peg I've ringed in the handle right side. You have to make sure you route the wires properly and don't pinch or catch them. It's easier than it sounds.
You'll know when you've done it because it feels right.
Now you have to place the end of part no. 2 WITHOUT the screwdriver slot in 2a in the right side. The other end of part 2 (WITH the screwdriver slot) has to go into hole 2b when you bring the 2 sides together.
Before you try to join the 2 siders make sure peg no. 3 aligns with slot 4 in the handle left side.
Now you have to KEEP THE RIGHT SIDE VERY FIRM so the twist spring doesn't drop off its peg and keep part 2 roughly in position and bring the handle left side up against the right. If you're gripping fairly tightly around the upper/middle of the handle things there will stay in place and you can get a little screwdriver and pop part 2 into its correct position.
Then just screw it together and pull off your sticky tape.
You will probably take 4 or 5 goes to get it right - I did - but you KNOW when it's OK by the look and feel. And your twist should now centre ;-)
BTW part 2 can be turned using a screwdriver in the aforementioned slot (from the left) for games without a rudder - it makes the twist solid.
