A 2-0 home defeat to MK Dons was Boro's 18th in their last 25 games and ensured they finished 18th in League One, six points clear of the drop zone.
Three successive losses brought a disappointing end to Westley's five-match spell since taking charge at the end of March.
He said: "In a lot of respects we are fortunate the season has ended as it did. I have had five games here and what I've watched is a side that is not fit enough, lacks the basics, and doesn't defend with a sense of professionalism or attack with drive and sense of belief. I am glad we got the points early and got ourselves out of trouble.
"Everybody at the football club knows that there is a lot of work to do. I don't plan on standing in the dugout and watching that ever again.
"We can't keep anything going. We've got no fitness in our bodies. It worries me trying to get points against better sides.
"I've bit my tongue and tried to be constructive with the lads but I've not enjoyed coming in day in, day out and working with the attitudes that are there. There's so much that needs to improve, there really is.
"There are people who are going to have to change their attitudes and players that have to leave. A rebirth is needed. There are some very, very good players in there who aren't at the level they're capable of. The basics aren't there.
"We haven't got the ability to put one foot in front of the other and if you can't do that you can't play football.
"I don't want to convince anyone who was here that there was anything positive about that (performance). The only positive is it's the end of the season and a chance to start again. I will not watch that level of contribution."