Yes, polarity is correct, but leads are far too long IMHO. Now you have created an ugly and mechanically unstable solution.
I would have bent out the wires 90 degrees directly at the base, and let them stick out no more than a few mm, outside of the base of the capacitor, so that the cap can be soldered flush to the PCB, just like the "tophat shaped" SMT elco it replaces, which has very similar leads, only flattened.
the black stripe on the cap with the minus sign denotes the negative lead, the straight side of the tophat elco denotes negative, with the "rooftop" side being the positive side.
The solder joints seem to have been soldered with a colder than ideal solder iron, and/or not enough solder flux, and have not flowed properly, its what we call a "cold joint", especially the negative lead, next time apply more heat and solder flux.
This elco delivers short pulses of increased current, to the RPI, so that these current pulses do not have to travel through the power supply lead, but can be supplied locally. This improves stability of the system, but strictly spoken, with thick land short USB supply leads it not 100% necessary.