you need more overlaps between the groups so that there are some red herrings.
also the answers it accepted were useless.

Good advice from Oli.Dont give up

It's surprisingly tricky to set an easy grid which isn't too obvious. Don't worry too much about answer acceptance. Even experienced setters often come in for criticism on that score. But Oli's other advice is good. I reckon if you can get in two lots of five confusable items you hit the jackpot. Six is too much for most humans to sort out in three minutes. Good luck.

Toast is spot on with the advice. The aim is to baffle without being to reliant on obscure knowledge. Nice effort.