One note: make bends on your jumper wires before soldering as heat will make them brittle and they will break easily if you need to re-bend them too close to solder point. Because of this I make my jumpers bit longer then needed and pre-bend them to their approximate ending shape.
Second thing that can be different from diagram is the adjustable linear 100K resistor. I had one that I had to rewire because the zero resistance was on the wrong end pin, the middle pin will always be same. You want to start from highest resistance and ending at the lowest resistance.
Third got ya is the 3 pin jack for electro-output leads, 2 pins make closed circuit connection as long as plug is not inserted - on these you have one that will always have connection even when plug is in (from pin 1 jumped to pin 6 on the LM358 chip), and the other will be disconnected -> this second one is connecting to the 22uF capacitor for the battery level display LED (only ON if the plug is out of jack and when battery has enough power remaining)
The 3rd pin on the jack is from LM358 pin 7 (after the 820 resistor and the variable 100k resistor).
Fourth problem can surface if one is not soldering correctly.
To reach tight spots on the board it is best to have soldering iron with small sharp point. Before you begin soldering always clean your soldering iron tip on a wet cloth or paper towel. The point should have solder on it (tip should look silver).
Solder should be all around the pins - proper soldering is done by having soldering iron contacting both the lead from the soldered component and the circuit board - then place flux core solder closest to the junction of lead and circuit board - best is not to touch the soldering iron with solder - this will guarantee that soldering points are hot enough to melt the solder - allowing acid flux to clean the area and then the melted solder replaces the acid flux. Soldering with acid flux core creates fumes that should not be breathed in to your lungs. Having small fan blowing slowly from one side of you will push these fumes away from you.