为什么我的ggplot的y轴比例错误？

Question

我正在使用frankbi杂草价格数据的串联版本（原始版本为https://github.com/frankbi/price-of-weed，清洁版本为https://github.com/Travis-Barton/Github_code）。我将HighQ / MedQ / Lowq的直方图转换为密度线。然后，我尝试在ggplot环境中将这些密度线相互叠加绘制，但我的坐标轴全都错了。

这是我应该拥有的：

这就是我最终得到的：

为什么ggplot缩放我的x轴？下面是我的代码

dat <- marijuana.street.price.clean



hist(dat$HighQ)
hist(dat$MedQ)
hist(dat$LowQ)

plot(1, ylim = c(0, .02), xlim = c(0, 800))
lines(density(dat$HighQ), lwd = 3, col = 'green', lty = 2)
lines(density(dat$MedQ), lwd = 3, col = 'yellow', lty = 2)
lines(density(dat$LowQ, na.rm = T), lwd = 3, col = 'red', lty = 2)


dat2 <- data.frame(indexH = density(dat$LowQ, na.rm = T)$x,
                   propH = density(dat$HighQ)$y,
                   indexM = density(dat$MedQ)$x,
                   propM = density(dat$MedQ)$y,
                   indexL = density(dat$LowQ, na.rm = T)$x,
                   propL = density(dat$LowQ, na.rm = T)$y
                   )

ggplot(dat2) + 
  geom_line(aes(y = propH, x = indexH, colour = "High")) + 
  geom_line(aes(y = propL, x= indexL, colour = "Low")) + 
  geom_line(aes(y = propM, x = indexM, colour = "Medium"))