The home side had taken the lead after less than ten minutes when flanker Akapusi Qera latched onto a pass from Arr at the scrum and ran 30 yards unopposed for a try.
However, the scrum half hit back when he dived over for a try deep into first half stoppage time on the way to a 13-13 draw for Warriors.
"When they scored the try from my pass everything definitely slowed down and there was nothing I could do, I was very disappointed in myself. It was a basic error from me and a bit of luck for them," said Arr.
"After it happened I said to myself it's going to take a big effort to pick myself up, after what happened after five minutes or so, but I felt I did that.
"The forwards put in a massive effort down on the Gloucester line on three or four occasions towards the end of the first half and I was just glad to get over and try to make up for what happened earlier.
"We did really well in the first half after conceding the early try," added Arr. "The boys worked really hard to get back into the game and get ahead before half-time.
"It's desperately disappointing to let the late try in with seconds on the clock to go. But it was a big response from us today, after what happened against Northampton, and you can't point the finger of blame at anyone.
"We will learn from the mistakes we made against Gloucester now and look to put it right against London Irish.
"If we perform on the day, like we know we can, it will be some game and hopefully four points instead of two."