After being shut-out in the first half, Ulster rallied through a penalty try and impressive young wing Rory Scholes, though Scarlets always kept them at arm's length and a late Aled Thomas penalty denied the Irish province a bonus point.
It came after a fine opening-game victory over the Ospreys, but Doak has promised a response in time for Ulster's hosting of Benetton Treviso on October 2.
"That is not what Ulster and the team want to be reflected at," said Doak. "That was not good enough for us and I am pretty disappointed with that.
"Our ill-discipline with the ball killed us. We had 12 turnovers in the first half and could not effect any change on the Scarlets at all.
"We had them pretty stretched at times and at 19-12 I thought if we keep going here we could get a draw out of it and maybe sneak it in the end, but it was not meant to me.
"There are a couple of things we need to look at again. The scrum area, which we had issues with last week. I am not sure whether it is something on us, we will have a look at the video and see what a true reflection of the game is."
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