Hello, when I do the approach and am just over the runway I get a missed approach / waypoint box on screen. What am I doing wrong, it doesn't give me the chance to land before saying go around. 

Hi, I think this is normal and should be documented in the Garmin User's Manual?

Basically, it is the GTN pre-loading the next possible step, that is missed approach, so that you just have to touch the screen to proceed.

Ok thanks for the quick reply, I will ignore it.

From what I have noticed, if you just ignore it completely, land your plane and slow down to taxi speed, the message will disappear automatically.

You can then just look at your GTN for the taxi map :-)