So if we finish all of our tickets early (which is often the case because measuring complexity is impossible to do up front), we're just supposed to sit around

So if we finish all of our tickets early (which is often the case because measuring complexity is impossible to do up front), we're just supposed to sit around until the sprint ends? A scrum master? Man, I thought my team was bloated with process but the fact that role exists elsewhere means I should probably be more grateful.