reduce or eliminate the empty zone in ggplot2 R

Question

I'm using gggenes to generate a plot

library(ggplot2)
library(gggenes)
df <- filter(example_genes, molecule %in% c("Genome1", "Genome2"))

just to generate a single gene line

df$molecule <- "Genome1"

head(df)

molecule gene start   end  strand orientation
1  Genome1 genA 15389 17299 reverse           1
2  Genome1 genB 17301 18161 forward           0
3  Genome1 genC 18176 18640 reverse           1
4  Genome1 genD 18641 18985 forward           0
5  Genome1 genE 18999 20078 reverse           1
6  Genome1 genF 20086 20451 forward           1

now to plot

p1 <- ggplot(df, aes(xmin = start, xmax = end, y = molecule)) +
    geom_gene_arrow() +
    theme_genes() + 
    geom_text(data=df %>% mutate(start = (start + end)/2), 
              aes(x=start, label = gene), nudge_y = -0.044, angle=70 ) +
    theme(axis.line=element_blank(), 
          axis.text.x=element_blank(),
          axis.text.y=element_blank(), 
          axis.ticks=element_blank(),
          axis.title.x=element_blank(),
          axis.title.y=element_blank(),
          legend.position="none",
          panel.background = element_blank(),
          panel.border=element_blank(),
          panel.grid.major=element_blank(),
          panel.grid.minor=element_blank(),
          plot.background=element_blank())

but I just want to reduce the size in y axis or eliminate the zone marked with a red X

my real problem is that I tried to merge 2 plots

 head(df2, 3)
  sample   size type
1   S300 135785    E
2   S306 135785    E
3   S314 135785    C
> 
> head(df3, 3)
  sample position nucl group
1   S300        1    G     0
2   S306        1    G     0
3   S314        1    -     0

plot

p2 <- ggplot(mapping = aes(y = sample)) +
    geom_col(aes(x = size, fill = type), data = df2) + 
    scale_fill_manual(values = c("grey68", "grey87"))  +
    geom_errorbar(aes(xmin = position, xmax = position), data = df3, size = 0.01, linetype = 1, alpha = 0.1, color = "black") +    
    #expand_limits(y= c(-((80*nrow(df_bar))/100), 1)) + 
    #coord_polar(theta = "x") + 
    theme_bw() + 
    theme(legend.position="none", #none 
          panel.background = element_rect(fill = 'white', color = 'white'), # background color "white"
          plot.margin = margin(grid::unit(0, "cm")),
          panel.border = element_blank(),
          panel.grid = element_blank(),
          panel.spacing = element_blank(),
          axis.title.y= element_blank(),
          axis.text.y = element_blank(),
          axis.ticks.y = element_blank(), # borrar las marcas en y  
          axis.title.x = element_blank(),
          axis.text.x = element_blank()) +
    guides(fill=guide_legend(nrow=1))

now merge both plots

library("cowplot")
plot_grid( p2, p1, align = "hv", ncol = 1)

I just want to reduce the empty (in X red) zone among both plots

How can I make it ?

Thanks so much