Standard ready mixed sand/cement (no ratios on bag 4:1?) Plus addition of
PVA, I slipped and put it bit much in I guess 100ml to 10mugs of dry mix.
Perhaps its not fully set yet.

Hmmm. I'm no expert, but I suspect you may have to redo it, with a bit more
lead in the wall. Also, how far do you go up before going into the wall?

For my conservatory flashing, IIRC, I went up just under 3 brick courses. I
then buried about 30mm (or however far a 110mm grinder will go) into the
existing mortar in an angle grinder slot and used silicone. No leaks that
I've detected. I made sure the slot was slightly upwards into the wall, so
any water drained outwards, not that it would have the chance with the
silicone, though.

Christian.