Radiator cap replacement

So, I bought a new radiator cap, but I think I bought the wrong one. I dont have the original one anymore, so I cant compare it again.

The one I bought looked to be the same size and it fits, but I think is too short because its not holding pressure through to the overflow bottle. Here is an example of what I mean.
https://i.imgur.com/ziQ9Pqu.png

Would someone be able to measure the overall height of their cap?

If it matters, I have a 2010 F650 GS.

I called my local dealer but they cant get a genuine one before Im taking the GS on a two week camping trip later this month.

Thanks

I bought a better quality cap, the Tridon CB15100 and that seems to have fixed the issue