You can use expand() to tweak your scale limits
library(ggplot2)
ggplot(iris, aes(Species, Sepal.Width)) +
geom_point()

ggplot(iris, aes(Species, Sepal.Width)) +
geom_point() +
scale_x_discrete(expand = c(0.05,0.05))

Created on 2019-04-07 by the reprex package (v0.2.1.9000)