If I'm not mistaken, you added the word "Total" in the last row of your data frame. So it is not a separate variable.
Easiest way in your case to compute both the total and the percentage at the same time, and bind them on the last row at once.
Note that it is unusual in R to put a total in a row of a data frame: basically the total is metadata (in this context), and the cells of the data frame should only contain data. You end up with columns that contain a mix of data and metadata. Once you are in this situation, you can't really work with the data frame anymore. I would recommend to keep your full data frame without additional row, and separately compute the Totals and percentage, and only print them together in the final output.