That is impressive. What you may need to bear in mind is that as the nuclear charge increases, all the electron orbitals move in closer to the nucleus. You may have been assuming, consciously or unconsciously, that the electron shells appear at a relatively fixed distance from the nucleus -- that is, that the n=1 shell is always at about the same distance from the nucleus, the n=2 shell is always at about the same additional distance, and so on.
Not the case! For example, if you take a look at the quantum mechanical model of the hydrogen atom and solve it for a "hydrogen-like" atom with atomic number Z and one electron (so, He+, Li++, Be+3,....,U+92 ha ha) then you will find that the average orbital radius of the electron scales like 1/Z. So if we ignored electron-electron repulsion entirely, the radius of each shell would decrease like 1/Z as Z increases. That's quite a contraction. It would mean that the n=1 shell in carbon, say, would be 1/6 the size of what it is in hydrogen. In the case of Ga, Z=31, the n=1 shell would be 1/31 the size it is in H! Each new shell would contract similarly.
So in the absence of electron-electron repulsion we would expect the size of atoms to shrink drastically as Z increases, going across the Periodic Table, and bumping up slightly at the beginning of each row with the addition of a new shell. Of course, real atoms do have electron-electron repulsion, lots of it, so the effect is considerably muted.
Nevertheless, the size of atoms does shrink considerably going from left to right in the Periodic Table, and it's worth remembering this is because all of the electron shells shrink, not just the valence shell.