Last Friday I finished printing the PCB.
I tried soldering the traces that were not connected properly and the silver trace melt away.
After that I went to the Voltera website and found out that their silver compound has a very low melting point and that they sell a low-melting-point solder to use with their boards.
I proceeded to make the circuit board on a perforated board.
Finished circuit
After the power rails were covered with electrical tape
I tested the circuit and it worked, except for the battery's T-plug. The plug was only making a connection when angled in a certain way and I could not fix it, so I decided to desolder it and solder one with the cables that came with it.
After that it worked perfectly. Tomorrow I will test the circuit with the electrodes.