No, Braveheart is not true, because there are a number of things in the movie that are not historically accurate, or that were embellished for the movie. Some dates in the movie are incorrect, and even down to some of the clothing that was not period clothing. It was a fun movie, but it wasn't the way it actually happened.
While there's no doubt that Braveheart is an entertaining movie it is not, by any stretch of the imagination, a factual documentary. William Wallace is a beloved historical figure in Scotland, and the movie is almost uniformly derided there for being inaccurate. While it's fun to imagine that's how things happened back then, they really didn't take place that way.