It may have happened if the candles you used were too oily. Some of the options you can try are:
use warm water (nice to do)
use gelatine to enhance the adhesion (nice to do), FYI, some of my customers dip candles in wax after they have applied decals
use a proper rubber squeegee and apply more pressure on the edges of decals (must do)
use warm water (nice to do)
apply another overcoats, especially on the edges, after the decal has completely dried
If you still have the same problem, try different brand candles.