Generally speaking, as works of art, movies reflect the work of multiple artists, including writers, directors, and cinematographers. Consequently, movies reflect the sensibilities and the technological capabilities of the moments in which they are created. Occasionally moviemakers will use a historical theme as a commentary on their own era. Researching the production details of the movie will help you better understand this aspect.
Movies themselves have certain parameters, such as the need to tell a complete story in a short amount of time, the need to create a narrative flow with a dramatic arc, and the need to tell complex stories using just images and sound. Ways that moviemakers accomplish this include
Compressing the timeline of the event to fit the length of the movie
Thinning the datamaking the story simpler
Focus more on the visually exciting or dramatic aspects of the event.
Minimize characters, combine historical personas into single characters, or adding characters.
Creating symbols and metaphors to stand in for complex ideas.
The above practices can be a starting point for your analysis of the movie. Rather than looking for errors, observe how the moviemakers had to negotiate between being true to the historical record, and crafting a dramatic narrative.