Air Behind Border In Corner--------Please Help------

[pompeyinlaspalmas]

I have put up some vinyl wallpaper in a bedroom and and also put a vinyl border overlapping the paper by 5 mm problem is in one corner the border has'nt stuck and you can look down the gap and i am afraid of putting pressure on it as it will tear.
Changing the whole border would be to much of a problem
Any help on what to do will be greatly recieved

Thanx