Deltaray - Sorry to hear about your channel imbalance issue.
I took a quick glance at your photos. Your wiring layout appears pretty good, but some of the solder joints are iffy.
20 and 21 look like classic cold solder joints. I would try reheating both of them until all the solder turns liquid, and then leave the soldering iron on them another 1-2 seconds or so until you see the solder flow into the joint.
I wonder whether the soldering issues are a function of your soldering iron? If your are using an iron with a large chisel point (or any large tip), that could make it difficult to make good contact. Unfortunately, most single-tip fixed wattage soldering irons come with such tips. I find large-tipped soldering points unusable for projects like this and instead use a soldering tip that is no more than 2mm (approx. 1/16 inch) wide at the tip. It works great.
Hope you getting it working soon.