Add upgraded legend to map ggplot

I have a MAP created with this code, and this file in MSEXCEL (LINK TO THE CORRESPONDING FILE): Add an upgraded legend to map ggplot:

This map contains information about qualifications of languajes by municipalities(MUNICIPIO), and thos municipalities were grouped in NEW_CD.

    library(tidyverse)
    library(brazilmaps)
    library(ggspatial)
    library(dplyr)
    library(data.table)
    library(hablar)
    library(readxl)
    library(stringi)
    library(grid)
    library(mapproj)
    library(rgdal)
    library(ggsn)

data <- read_excel("2005.xls") %>%
  mutate(MUNICIPIO = padroniza_texto(MUNICIPIO)) %>%
  inner_join(pop2017 %>% mutate(nome_mun = padroniza_texto(nome_mun)), by = c("MUNICIPIO" = "nome_mun")) 

<br>dados_para_mapa$mun <- replace(dados_para_mapa$mun, dados_para_mapa$mun < 3500000, NA)
<br>dados_para_mapa$mun <- replace(dados_para_mapa$mun, dados_para_mapa$mun > 4000000, NA)
<br>dados_para_mapa<-dados_para_mapa[!is.na(dados_para_mapa$mun), ]

<br>dados_para_mapa <- read_excel("2005.xls") %>%
  mutate(MUNICIPIO = padroniza_texto(MUNICIPIO)) %>%
  inner_join(pop2017 %>% mutate(nome_mun = padroniza_texto(nome_mun)), by = c("MUNICIPIO" = "nome_mun")) 

<br>dados_para_mapa$mun <- replace(dados_para_mapa$mun, dados_para_mapa$mun < 3500000, NA)
<br>dados_para_mapa$mun <- replace(dados_para_mapa$mun, dados_para_mapa$mun > 4000000, NA)
<br>dados_para_mapa<-dados_para_mapa[!is.na(dados_para_mapa$mun), ]
<br>dados_para_mapa %>% find_duplicates(MUNICIPIO)

    get_brmap("City", geo.filter = list(State = 35)) %>% 
     <br> left_join(dados_para_mapa, c("City" = "mun")) %>% 
     <br> group_by(NEW_CD) %>%
     <br> summarise(
     <br>   VARIAVEL = mean(COEFICIENTE_DE_DETECCAO)) %>%
     <br> ggplot() +
     <br> geom_sf(aes(fill = VARIAVEL))+
     <br>  # change color pallet
     <br> scale_fill_continuous(low = "#ffffff", high = "#60DCCC") +
     <br>  #Escale
     <br> annotation_scale(location = "bl", width_hint = 0.5) +
     <br>  annotation_north_arrow(location = "bl", which_north = "true", 
     <br>                         pad_x = unit(0.5, "in"), pad_y = unit(0.5, "cm"),
     <br>                        style = north_arrow_fancy_orienteering) +
     <br>  # legend title
     <br> theme(legend.title = element_text(colour="black", size=15, face="bold")) +
     <br> # legend labels
     <br> theme(legend.text = element_text(colour="black", size=15, face="bold")) +
     <br> # erase cartesian system in background
     <br> theme(panel.grid = element_line(colour = "transparent"),
     <br>        panel.background = element_blank(),
     <br>       axis.text = element_blank(),
     <br>      axis.ticks = element_blank())
    <br>

as result, I have a map with a simple legend,

map without legend

but i need to upgrade this legend showing the mean and standar error for each grouping [group_by(NEW_CD)] instead each color box associated with each mean and the number of observations into each group [scale_fill_continuous(low = "#ffffff", high = "#60DCCC")].

map with legend (WANTED)

I hope to be clear and be helped. Map annotation needs to be clear.

Advance Thank you very much.