The Cherries saw Villa score three of their four goals on Sunday from set plays – the first was an excellent free kick from Emi Buendia, before their third and fourth goals came from corners.
The third saw Ross Barkley glance a header home at the far post, before a Youri Tielemans shot from the edge of the box was diverted past Djordje Petrovic by Donyell Malen for the fourth.
Asked about the four goals Bournemouth conceded, Scott told BBC Radio Solent: “It's unacceptable, especially the set pieces.
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“I mean, the free kick, maybe just a bit of lapse of judgement from Alex [Jimenez] and they get the free kick and it's a lovely finish for that one.
“And Onana's goal as well, obviously a great goal. And then the set pieces, we spoke a lot during the week because at Man City there were little things that we got away with, to be honest.
“Tommy [Elphick] took it through with us and we got away with a few at Man City, so we were a lot better in our set pieces in training.
“We're focused on them and something's just not gone right again today. Lack of focus maybe, I don't know, but yeah, it's not good enough.
“You can't concede two set pieces and hope to win games in the Premier League. So it's definitely something that we've got to keep working on and really focus for ahead of West Ham.”