Return the parts and get “direct fit” OEM replacement parts. You simply have the wrong parts.
Were you to install the smaller resonator, it would very likely change the tone of the exhaust, perhaps even the volume (but not necessarily). The volume would only change if the waves were modified in a manner such that they were allowed to combine their energy creating higher peaks at the cost of modifying the stability of the frequency out. Resonators cannot create energy to raise amplitude, but they can if designed to do so cause the waves’ to pile onto one another somewhat. That typically creates an unstable output waveform.
Every time your exhaust valve opens, a pulse of energy travels out the combustion chamber and down the pipe. The exhaust stream is a constant series of pulses, waves of energy in the air. A resonator works by allowing those waves to bounce around inside the can, even push against one another and cancel one another out to some extent, and the waves that go out the resonator toward the tailpipe are thus modified. How the waves are modified becomes a function of how they’re allowed within the resonator to expand, how the resonator directs the waves, how long and wide the resonator is (the dimensions affect the wave propagation) and other acoustic factors designed into the resonator. Exactly how a given resonator affects the waveform can vary depending on the resonator’s design.
A typical stock resonator is designed to “calm” the waveform, reducing the peak amplitude but creating a smoother sound. It “chops” the peaks in the soundwaves, and fills in the “valleys” with their energy, allowing the “valleys” to rise a bit.
If you were happy with the car’s sound when new, the best approach by far is to use an exact replacement. A “direct fit” OEM replacement part will give you that. It’ll also make installation much easier.
I hope this helps you to understand how they work as well as encourages you to return the parts you have for the proper ones.