United were leading 4-3 with goals from Bruno Fernandes and Matheus Cunha in two minutes before Eli Junior Kroupi struck the final equaliser for Bournemouth.
Amorim said, "It was a fun game for everyone at home. I think we started really well. We did a good first half.
"The result should be completely different. And then again, six minutes of the second half, similar to Nottingham (Forest), we lost the concentration, and they score two goals.
"But we managed to get back to the game, we scored two goals again, and then we have to finish the game. Just a throw-in in our possession, we have to close and think about not to go again, to stay calm and close the game.
"I saw the effort of the players, I saw the effort of the defence, and at the end of the game, you make 4-3, I had the feeling that we would continue to push and score another one. We tried but in the end it was a draw.
"A lot of good things, but a lot of things to work (on). We are not winning games sometimes in the details. It's not because it's a back four, back three, back five.
"It's the details that we need to work, understand the momentum of the game and we need to be clinical. Again, today against a very good team, we created many chances to win the game, and we should have won the three points."