Hello. 

I have made a Chronurgy Wizard which is now at lvl 10, and really enjoying it. 

However, I have noticed that among the Dunamancy spells, I only have access to the Graviturgy spells in the spell list. 

I might have missed something, but I am not sure the rules actually say only graviturgy for graviturgists and vice versa. 

I believed that dunamancy in general would be available for dunamancers from the get-go, with additional rules for dunamancy spell availability for other wizard schools (non-dunamancers) should the DM be willing. But I do not understand the Chronurgists and graviturgists only having access to a part of the dunamancy list repsectively. It makes sense intuitively, but I thought the rules allowed for complete dunamancy availability. 

Anyone able to help me understand this, or if WOTC have made a mistake in the character builder?

Works 100% correct to the RAW for me, so I'm guessing your issue is due to homebrew. Somebody in your campaign (homebrew is automatically shared with everyone) may have added the Graviturgist spells to Chronurgy subclass for example. 

Add one of the Graviturgist spells and on your character sheet click it. In the sidebar that opens it will either have "Source" or "Version". If it has Version it is a homebrew version of the spell.

EDIT

OK, I think I misread your post. I thought you said you were getting Graviturgy spells showing when you were Chronurgy, but it seems you mistyped and mistakenly believe either subclass should get access to all dunamancy spells. This is incorrect. Some spells are both, some are Chronurgy only and some are Graviturgy only. The list in the book denotes * for Chronurgy, ** for Graviturgy and no asterisk for both. 

The list, in more clarity:

The only way to get both lists, or to get Dunamancy spells on a regular caster - is to homebrew the subclass and add those spells to the spell list of the homebrew subclass.