The hosts led 3-0 only to see their lead cut to 3-2 before holding on to clinch victory after a thrilling finish.
"I thought we deserved a point for the way we came back, we showed a lot of character and could have easily got something from the game," Parkinson said.
"But we left ourselves with too much to do. We should have never gone three goals behind, we conceded some bad goals.
"We've had a good start to the season but we should be performing better against a side like Dagenham. No disrespect, but we weren't at the races in the first half.
"We knew it was going to be a tough game, but I'm disappointed we've not got anything from the match."