Add country names to map in ggplot

I try to make a map in ggplot of South America and the number of cases.
I would like to add the name of the countries.

However, it is difficult to add the number of cases in the legend and the names of the countries.

library(ggplot2)
library(dplyr)

sa.countries <- c('Argentina', 'Bolivia', 'Brazil',  
               'Colombia', 'Chile','Ecuador','French Guiana','Guyana', 
               'Paraguay', 'Peru', 'Suriname', 
               'Trinidad and Tobago', 'Uruguay', 'Venezuela')

countries.maps <- map_data("world", region = sa.countries)

country.cases <- tribble(~region, ~papers,
                          'Argentina', 33, 'Bolivia', 8, 'Brazil', 242,
                          'Colombia', 41, 'Chile', 9, 'Ecuador', 44,
                          'French Guiana', 3, 'Guyana', 0, 'Paraguay', 1,
                          'Peru', 8, 'Suriname', 0, 'Trinidad and Tobago', 2,
                          'Uruguay', 0, 'Venezuela', 7)

df.country <- left_join(countries.maps, country.cases, by="region")


ggplot(df.country, aes(long, lat, group = group))+
  geom_polygon(aes(fill = papers ), color = "white") +
  scale_fill_viridis_c(name='# cases', option = "C") +
  coord_equal() +
  theme_bw()

Here is an example of the map as it should be

Thanks in advance.

You may try

dff <- df.country %>%
  group_by(region) %>%
  summarize(long = mean(long, na.rm = T), lat = mean(lat, na.rm = T), group = group)
ggplot(df.country, aes(long, lat, group = group))+
  geom_polygon(aes(fill = papers ), color = "white") +
  scale_fill_viridis_c(name='# cases', option = "C") +
  coord_equal() +
  theme_bw() +
  geom_text(data = dff, aes(long, lat, label = region, group = group), size = 2)