We usually say "get in line" (without the article "the"). Similarly, we say "be in line", "stand in line", or "wait in line".
If we're not identifying a particular line, we say "get in line" (without the article "the").
We got in line for the attraction.
Similarly, we say be in line, stand in line, or wait in line.
We had to wait in line for an hour.
When using the phrase "cut in line", leave out the article as well. We use this expression when someone goes in front of other people who are already waiting in line.
They cut in line in front of us.