The result leaves Blues at the bottom of Pool 2 with a final fixture against Harlequins at the Arms Park on Friday night to come.
But John believes Blues could have taken even more away from the West Country with more of a killer instinct as they played some inventive and flowing attacking rugby at times with no end product.
"I feel a little bit disappointed as we had a couple of chances in that game and we didn't finish them off," said John.
"It was nice to score at the end to bring us to 13 points, but ten minutes before that it could have made it a six point game.
"I'm disappointed that we managed to get into those situations and not capitalise on them.
"The boys just need to be a little bit more clinical, cut out the errors and work on tactical timing and it would have been a different score again. It would have been a little bit closer to what the final score was.
"Individuals might have personal disappointments, hopefully they will have another opportunity to play next week against Quins to put things right and make less errors. There was a lot of opportunity created out there."
"I don't want to single anybody out, but we attacked where we wanted too," he added
"The boys stepped up. Some of the boys had their first-ever game at that level and Ellis Jenkins captained for the first time at this level.
"We created chances that should have got us a lot closer. Over all disappointed that we lost a game but there were a lot of good things in it. But not enough good things to make it a win."