Plot appears much different in knitted HTML than in RStudio

[Ness329]

I am trying to knit my code into an HTML file however when I do so the resulting graph appears much differently than the one produced in R studio(see image)
My code is as follows:

p6 <- airquality %>%
     ggplot(aes(Month, Solar.R, fill = Month)) + 
     ggtitle("Solar Radiation") +
     xlab("Month") +
     ylab("Radiation Level") +
     geom_boxplot() +
     scale_fill_discrete(name = "Month", labels = c("May", "June","July", "August", "September"))
p6

[HanOostdijk]

Yes, I see.
Referring to Struggling to knit chunk to HTML or Word :
in the left you have used the factor(Month) for the x axis and in the right plot you did not