Bubble map with ggplot shows bubbles on borders

I want to make a bubble map using ggplot. The current map I have looks like this, I want to add bubbles that represent the number of births in each region (regions that have more births would have a much bigger bubble):


I made the map using the following code:

ggplot() +
      # county polygons
      geom_polygon(data =shapefile_df, aes(fill = mean_birth_weight,
                                               x = long,
                                               y = lat,
                                               group = group), colour  = "black") +
      # county outline
      geom_path(data = shapefile_departamentos, aes(x = long, y = lat, group = group), 
                color = "black", size = 1) +
      coord_equal() +
      scale_fill_distiller(palette = "RdYlGn", direction=1, breaks = c(2600, 2700, 2800, 2900, 3000, 3100,  3200, 3300, 
                                                                       3400,  3500), limits = c(2600, 3600), na.value = "black") +
      theme_bw() +
      theme(panel.grid.major = element_blank(),
            panel.grid.minor = element_blank(),
            panel.border     = element_blank(),
            axis.title       = element_blank(),
            axis.text        = element_blank(),
            axis.ticks       = element_blank())

But when I tried to add geom_point to it, the map that resulted it, looked like this:

My guess is that bubbles were drawn in the borders of the map, but there are a lot of them. The code I used for the last map was this:

ggplot() +
      # county polygons
      geom_polygon(data =shapefile_df, aes(fill = mean_birth_weight,
                                               x = long,
                                               y = lat,
                                               group = group), colour  = "black") +
      geom_point(data = shapefile_df, aes(x=long, y=lat, group = group, size = Total))+
      # county outline
      geom_path(data = shapefile_departamentos, aes(x = long, y = lat, group = group), 
                color = "black", size = 1) +
      coord_equal() +
      scale_fill_distiller(palette = "RdYlGn", direction=1, breaks = c(2600, 2700, 2800, 2900, 3000, 3100,  3200, 3300, 
                                                                       3400,  3500), limits = c(2600, 3600), na.value = "black") +
      theme_bw() +
      theme(panel.grid.major = element_blank(),
            panel.grid.minor = element_blank(),
            panel.border     = element_blank(),
            axis.title       = element_blank(),
            axis.text        = element_blank(),
            axis.ticks       = element_blank())