Henry Pyrgos hit-back for Scotland but South Africa held strong to consign the hosts to a fourth straight defeat at Murrayfield and end their hopes of climbing into the second tier of nations in the world rankings.
"We've got a lot to learn in improving defence and in attack, particularly physically," said Robinson.
"I felt they bullied us a little in the first half. They didn't have to do a lot to win the game because we gave them field position from penalties.
"They scored from a maul which makes me very, very angry and then from an interception.
"I thought South Africa defended superbly well. If they hadn't defended as well as they had, it could have been a different story.
"Henry Pyrgos brought some real energy to the field and he took his chance well.
"The try came off beautifully but we are all massively disappointed with the result. It's a game we should have got more out of.
"First half, we didn't come out like we wanted to and in the second half we had chances to get more points on the scoreboard and we didn't do it.
"There were times when we didn't hold on to the ball when we needed to and we weren't accurate enough at the breakdown.
"It was very quick and physical - a definite step up for me. But you just go back to what you know and try to concentrate on the things you can do well.
"The crowd has been amazing for both games at Murrayfield and we are disappointed for them."
Scotland host Tonga next week and Robinson has urged his side to produce a ruthless performance.
"Next week against Tonga we need a performance to put together the lessons they've learned from the first two games," added Robinson.
"There's a lot for us to look at. The disappointing thing from our side is we allowed a side to get a lead again and that's something you can't afford to do.
"It's going to be a huge week of training for Tonga. We need to go and get the win."