Grounded coplanar waveguide differential gap
The manufacturer's recommended layout looks strange to me. I would have expected to see a differential pair coming out of the balanced ports.

Having said that, I think you're OK either way for the distances involved in your design. I would have used a tightly coupled differential pair right out of the balun, unlike what you currently have. It may give you some additional crosstalk/interference protection. Pay special attention to the presence of ground vias as close as possible to the ground pins (2, 5). 

Also, when designing the transmission lines keep in mind you want Zdiff=50Ω. In the case of the weakly coupled lines out of the balun before the caps, this translates in Zo~25Ω for each line individually. In the case of a tightly coupled pair, like you currently have between the caps and the mixer, Zo may have to be somewhat higher than 25Ω, so that you achieve Zdiff=50Ω.

One more comment: the lines between the caps and the mixer don't seem to be properly length matched - the outer trace within each pair looks a little longer to me.