Selecting a range of values in a specific column for R ggplot

I am trying to select a range of values (i.e. the first 4 values) in a specific column from a table. The column is called "RL45". I tried the following code to create a plot in ggplot:
newplot <- ggplot(data = GEV, aes(x = RL45[1:4])) + geom_density(color = "midnightblue") + xlab("Location (mm/day") + ggtitle("Global Location under RCP4.5") + xlim(300, 350)

This results in this strange error:

Error: Aesthetics must be either length 1 or the same as the data (34): x

This is odd, as I selected the first 4 values in that "RL45" column.
Any thoughts would be greatly appreciated!
Thank you,
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