There are companies out there that will print you white water slide decals. One charges around £50 for an A4 sheet which is "double pass" Ideal if its going on a black background as the white stands out more. The single pass, around £28 a sheet is a bit opaque.
I think your geometric pattern turned out really well. I've not used it personally but one of the lads at work swears by Frog tape when decorating as you wet the edge once you've applied it and it creates a better seal. That should prevent and bleeding under the tape.