Impedance line matching and component value matching
I don't think you are following the rules set out in the document closely enough. For a start here is a link that opens up a document that describes the device. Here are the critical things rolled into one picture: -



I'm not saying that how you've mounted the interface circuit won't work but if it doesn't then you'll kick yourself for having to buy a new PCB. Also they have the groundplane extending to 2.5mm from the edge of the antenna - I think you should do the same for the reasons above. As @ThePhoton points out, it's unlikely that such a short feedline is going to give problems BUT/HOWEVER following the instructions in the data sheet is realistically your only course of action and if it says 50 ohm impedance tracking then go for it.