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According to the diagonal relation, $\ce{Na}$ and $\ce{Ca}$ have similar radii. $\ce{Na+}$ and $\ce{Ca+}$ have thus similar radii as well but, when one more electron is removed from $\ce{Ca+}$, making it $\ce{Ca^{2+}}$, its effective nuclear charge increases, which will make its radius decrease.
What you're missing is that the electron (or rather, Bohr's version thereof) moves in a curved path because of the centripetal force provided by electrostatic attraction to the proton. You therefore have $mvr=nh/2\pi$, quantized angular momentum and $mv^2/r=\epsilon_0e^2/r$ centripetal force from electrostatic attraction For each quantum number $n$ we ...