title: hjust not working properly to center my title in ggplot2 in R
body: <p>I am new to R. I am having issues centering my title in <code>ggplot</code> using <code>hjust</code> and I am not sure what I am doing wrong. Here is my following code and bar plot. Any assistance would be greatly appreciated. </p>
  
  <pre><code>ggplot(mentalsum, aes(x=task, y=mental, fill = task)) + 
    ggtitle( "NASA-TLX Mental Demand") + 
    theme(plot.title = element_text(hjust = 0.5)) + 
    geom_bar(position=position_dodge(), stat="identity") +
    geom_errorbar(aes(ymin=mental, ymax=mental+se),
                  width=.2,                    # Width of the error bars
                  position=position_dodge(.9)) + xlab("Task") + 
    ylab("Weighted Ratings") + 
    labs(fill= ("")) + 
    theme_classic()
  </code></pre>
  
  <p>Best,</p>
  
  <p>Chris </p>
  
  <p><a href="https://i.stack.imgur.com/raVKz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/raVKz.png" alt="enter image description here"></a></p>