Adjusting space between clusters on clustered bar chart with multiple x-axis labels

I am having issues with the following plot:

I cannot seem to change the space between the two clusters. I would like the bars in each cluster to touch each other as they are now, but to add additional space between the clusters. I have tried numerous solutions, including position_dodge() etc, but they don't make a difference to the appearance of the plot. Is it because there are two levels on the x-axis?

Here is my data:

results <- dput(results)
structure(list(tdcs = c("active", "active", "active", "active", 
"active", "active", "sham", "sham", "sham", "sham", "sham", "sham"
), type = structure(c(2L, 2L, 3L, 3L, 1L, 1L, 2L, 2L, 3L, 3L, 
1L, 1L), .Label = c("Comprehension", "Trained Words", "Untrained Words"
), class = "factor"), chgacc = c(0.693669355, 0.512145161, 0.189221837, 
0.19727383, 0.488085538, 0.080855379, 0.365701923, 0.331008065, 
-0.405006036, -0.210909879, -0.135833333, 0.006145503), grouping = c("Active: 1 Month Post", 
"Active: 3 Months Post", "Active: 1 Month Post", "Active: 3 Months Post", 
"Active: 1 Month Post", "Active: 3 Months Post", "Sham: 1 Month Post", 
"Sham: 3 Months Post", "Sham: 1 Month Post", "Sham: 3 Months Post", 
"Sham: 1 Month Post", "Sham: 3 Months Post"), time = c("1 Month Post", 
"3 Months Post", "1 Month Post", "3 Months Post", "1 Month Post", 
"3 Months Post", "1 Month Post", "3 Months Post", "1 Month Post", 
"3 Months Post", "1 Month Post", "3 Months Post")), row.names = c(NA, 
-12L), spec = structure(list(cols = list(tdcs = structure(list(), class = c("collector_character", 
"collector")), type = structure(list(), class = c("collector_character", 
"collector")), chgacc = structure(list(), class = c("collector_double", 
"collector")), grouping = structure(list(), class = c("collector_character", 
"collector")), time = structure(list(), class = c("collector_character", 
"collector"))), default = structure(list(), class = c("collector_guess", 
"collector")), skip = 1L), class = "col_spec"), class = c("spec_tbl_df", 
"tbl_df", "tbl", "data.frame"))

And my code:

library(tidyverse)
library(cowplot)

results$type <- as.factor(results$type)


colorpicks <- c("darkslategray", "azure3","blue3", "cyan")


plot <- results %>%
  dplyr::filter(type == "Trained Words") %>%
  ggplot(aes(x = time, y = chgacc, fill = grouping)) +
  theme_minimal_hgrid()+
  geom_col(position = position_dodge(0.9), width = 1) + 
  facet_wrap(~tdcs, strip.position = "bottom", scales = "free_x" ) +
  scale_fill_manual(values = colorpicks, labels = c('Active - 1 Month Post','Active - 3 Months Post',
                                                    'Sham - 1 Month Post', 'Sham - 3 Months Post'))+
  theme(panel.spacing = unit(0,"lines"),
      strip.background = element_blank(),
      strip.placement = "outside")+

  scale_y_continuous(labels = scales::label_percent(accuracy = 1),limits = (c(-.2,.7))) +
  labs(x = "Stimulation Type", y = "Mean Accuracy \nChange from Baseline", fill = 'Stimulation Type & \nTime Point')+
  theme(plot.title = element_text(size = 16),
        strip.text = element_text(size = 16), 
        axis.text = element_text(size = 12),
        axis.text.x = element_text(angle = 90, vjust = 0, hjust = 1),
        axis.title.y = element_blank(),
        axis.title.x = element_blank(),
        legend.text=element_text(size=11))
plot

To add more space between your clusters you could increase the expansion of the x scale using e.g. scale_x_discrete(expand = c(0, 1.2)) which doubles the default expansion:

library(tidyverse)
library(cowplot)

results %>%
  dplyr::filter(type == "Trained Words") %>%
  ggplot(aes(x = time, y = chgacc, fill = grouping)) +
  theme_minimal_hgrid() +
  geom_col(position = position_dodge(0.9), width = 1) +
  facet_wrap(~tdcs, strip.position = "bottom", scales = "free_x") +
  scale_fill_manual(values = colorpicks, labels = c(
    "Active - 1 Month Post", "Active - 3 Months Post",
    "Sham - 1 Month Post", "Sham - 3 Months Post"
  )) +
  theme(
    panel.spacing = unit(0, "lines"),
    strip.background = element_blank(),
    strip.placement = "outside"
  ) +
  scale_y_continuous(labels = scales::label_percent(accuracy = 1), limits = (c(-.2, .7))) +
  scale_x_discrete(expand = c(0, 1.2)) +
  labs(x = "Stimulation Type", y = "Mean Accuracy \nChange from Baseline", fill = "Stimulation Type & \nTime Point") +
  theme(
    plot.title = element_text(size = 16),
    strip.text = element_text(size = 16),
    axis.text = element_text(size = 12),
    axis.text.x = element_text(angle = 90, vjust = 0, hjust = 1),
    axis.title.y = element_blank(),
    axis.title.x = element_blank(),
    legend.text = element_text(size = 11)
  )