Westley was sacked by Preston in February, just over 12 months after leaving Stevenage for Deepdale, but he returned with a win as Ehmer, on loan from QPR, struck in the 76th minute.
Boro's season is all but done with no relegation worries and no chance of reaching the play-offs.
However Westley insists Boro must finish strongly if they are to challenge for promotion next season.
"It's nice to be back and it's nice to be back with a win, it was a really welcoming afternoon from the fans, everybody at the club was pleased to see me back - that was the feeling I got," he said.
"We want to make sure going into next year that people are looking at Stevenage and thinking Stevenage are a difficult side to play against and a side that normally wins its games.
"So if we can use these four games to set the scene, and with the attacking intent we've got in the squad, then we'll be a difficult proposition for sides to play against.
"The players put on a really strong performance, it was gritty, it was strong, it was organised and considering they have only had a couple of days to get ready after the Crawley game to take on a new manager I think they were outstanding."