How to reverse order of x-axis breaks in ggplot?-CodePudding

I'm trying to make a plot wherein large values on the x-axis are actually small, and vice versa. Because of how ggplot reads the data, it's automatically ordering the data such that the x-axis is ordered smallest to largest, and I'm trying to figure out how to reverse that.

I ended up reversing the actual order of the data by using rev(), but that won't change where the breaks in the x-axis are.

For example:

library(tidyverse)

# Making fake data
Freq <- rep(c(1, 2, 3, 5, 10, 15, 20), 10)
SD <- c(rep(1, 7), rep(2, 7), rep(3, 7), rep(4, 7), rep(5, 7), rep(6, 7), rep(7, 7), rep(8, 7), rep(9, 7), rep(10, 7))
Intro_0 <- sample(80:120,135,TRUE)
Intro_0 <- c(seq(80, 74, -1), seq(78, 72, -1), seq(76, 70, -1), seq(74, 68, -1), seq(72, 66, -1), seq(70, 64, -1), seq(68, 62, -1), seq(66, 60, -1), seq(64, 58, -1), seq(62, 56, -1))
test2 <- data.frame(cbind(Freq, SD, Intro_0))

# Plotting
# Here's where I reverse the order of the data: "rev(Freq)"
ggplot(test2, aes(rev(Freq), SD, z = Intro_0))  
  geom_contour_filled(bins = 9) 
  scale_fill_brewer(palette = "BuPu") 
  labs(x="Frequency", 
       y="Magnitude",
       title="Test Plot") 
  # Here's where I *think* the issue is...
  scale_x_continuous(breaks = c(1, 2, 3, 5, 10, 15, 20), # I've tried rev() here
                     labels = c("Freq = 1/20", " ", " ", " ", " ", " ", "Freq = 1/1")) 
  # Aesthetic to clear up panel; can ignore
  theme_bw() 
  theme(panel.border = element_blank(), panel.grid.major = element_blank(), panel.grid.minor = element_blank(), axis.line = element_line(colour = "white")) 
  theme(axis.text.x = element_text(angle = 45, hjust=1), plot.caption.position = "plot", plot.caption = element_text(hjust = 0)) 
  labs(fill="Legend")

If you run the lines above, you'll find that the rev(Freq) reorders the data how I want it, but that the breaks in the x-axis still aren't ordered properly (the first three ticks are closer together, indicating the "1, 2, 3, ... , 20" (though the break labels are as I want them). I've tried reversing the breaks argument and a few other obvious fixes, but nothing's worked.

Let me know if you have any ideas! Thanks so much for any advice