I don't remember if Galactus was fully fed when he went against the In-Betweener. Most of the time he is not fully fed so I'm assuming he wasn't, but perhaps someone can clarify for me. If he wasn't fully fed, I think In-Betweener is kinda overrated DX

The In-Betweener is one of three Omnipotent Beings that, at full-strength, are supposed to be more powerful than anything else in the Marvel Universe. The other two are Galactus, and Eternity.
 
So yeah, I think In-Betweener stands at least an equal chance of beating Galactus as Big-G does of beating him.

saint of killers lol jk ummm thanos?

In betweener is the opposite of Galactus as in Cosmic vs Magic, Death and Eternity vs Order and Chaos etc."They are equal in most cases". 

" In betweener is the opposite of Galactus as in Cosmic vs Magic, Death and Eternity vs Order and Chaos etc."They are equal in most cases".  "

" The In-Betweener is one of three Omnipotent Beings that, at full-strength, are supposed to be more powerful than anything else in the Marvel Universe. The other two are Galactus, and Eternity.  So yeah, I think In-Betweener stands at least an equal chance of beating Galactus as Big-G does of beating him. "

"Was Galactus fully fed when he fought In-Betweener?"   No, he was not.  Galactus had just nearly died of indigestion when he faced the In-Betweener. 
 
Also,  when they fought the In-Betweener possessed the Soul Gem. 

" I don't remember if Galactus was fully fed when he went against the In-Betweener. Most of the time he is not fully fed so I'm assuming he wasn't, but perhaps someone can clarify for me. If he wasn't fully fed, I think In-Betweener is kinda overrated DX "

No

Nope.