3.2Relative minor is degree 6 of the major scale

In C major:

C D E F G A B

A is degree:

6

So the relative minor of C major is A minor.

In G major:

G A B C D E F♯

degree 6 = E

Therefore:

G major ↔ E minor

In D major:

D E F♯ G A B C♯

degree 6 = B

So:

D major ↔ B minor

This gives:

Major	Relative minor
C	Am
G	Em
D	Bm
A	F♯m
E	C♯m
F	Dm
B♭	Gm
E♭	Cm

This is exactly why your original chord chart had major and minor chords paired together around the outside.