Make R Plot Axes the Same for Multi-Plot Figure - r

Question

I have 3 multi-plot figures I'm making for a manuscript and R is shrinking the first plot in the 2 figures with 3 paneled plots. They have different axes and scales so I couldn't use a facet function, but ggarrange() does what I need. Is there a way to make the size of the actual graphs identical?enter image description here
Plot 1 axes smaller
Here's the script generating them:
library(ggplot2)
library(ggpubr)
library(ggpmisc)
library(ggrepel)
library(tidyverse)
summary_bp <- read.table("1500bp_amas_summary.txt", header=TRUE)
alignment_length <- summary_bp$Alignment_length
no_inf_sites <- summary_bp$Parsimony_informative_sites
Length_Site_Reg <- ggplot(summary_bp, aes(x=alignment_length, y=no_inf_sites)) +
geom_point(shape = 1, size = 1) +
geom_smooth(method = lm, size = 0.7) +
stat_regline_equation(label.x = 3000, label.y = 3500, geom = "text", aes(label= ..rr.label..), size = 2) +
stat_cor(method = "pearson", label.x = 3000, label.y = 3100,aes(label = ..p.label..), size = 2) +
coord_cartesian(xlim = c(1500, 15000), ylim = c(0,4000)) +
scale_x_continuous(breaks = seq(1500, 15000, by=1500)) +
scale_y_continuous(breaks = seq(0, 4000, by=500)) +
labs( x = "Alignment Lengths", y = "Number of Parsimony \n Informative Sites") +
theme(aspect.ratio = 1, axis.text.x = element_text(angle=45, hjust = 1),
axis.line = element_line(color = "black"), panel.background = element_blank(),
panel.grid.major = element_blank(),
panel.grid.minor = element_blank(),
axis.text = element_text(size = 7),
axis.title.x = element_text(size = 9, face = "bold"), axis.title.y = element_text(size = 8, face = "bold"))
Length_Site_Reg
#Fig. 3b) GC hist
summary_all <- read.table("summary_trim.txt", header=TRUE, sep = ",")
GC_hist <- ggplot(data = summary_all, aes(x=GC_content)) +
geom_histogram(binwidth = 0.025, fill = "white", color = "black") +
xlim(0.3,0.725) +
coord_cartesian( ylim = c(0,1050)) +
labs(x = "GC Content", y = "Number of Orthologs") +
theme(aspect.ratio = 1, panel.background = element_blank(), panel.grid.major = element_blank(),
panel.grid.minor = element_blank(), legend.position = c(0.75, 0.65),
axis.line = element_line(color = "black"), axis.text = element_text(size = 8),
axis.title = element_text(size = 9, face = "bold"), legend.key.size = unit(0.4, 'cm'),
legend.key.height = unit(0.4, 'cm'),
legend.key.width = unit(0.4, 'cm'),
legend.title = element_text(size=6),
legend.text = element_text(size=6)) +
geom_vline(aes(xintercept=mean(GC_content), color="mean"),
linetype="solid", size=0.5, show.legend = FALSE)
GC_hist
# Fig. 3c) K2P Divergence Hist
#trimmed_k2 <- file.choose()
trimmed_k2_data <- read.table("trimmed_alignment_k2.csv", header=TRUE, sep = ",")
trimmed_k2_data
trimmed_k2_data_hist <- ggplot(data = trimmed_k2_data, aes(x=distance)) +
geom_histogram(binwidth = 0.025, fill = "white", color = "black") +
coord_cartesian( ylim = c(0,1200) ) + scale_y_continuous(breaks = seq(0,1200,200)) +
labs(x = "K2P Distance", y = "Number of Orthologs", size= 3) +
theme(aspect.ratio = 1, panel.background = element_blank(), panel.grid.major = element_blank(),
panel.grid.minor = element_blank(),
axis.line = element_line(color = "black"),
axis.text = element_text(size = 8),
axis.title = element_text(size = 9, face = "bold")) +
geom_vline(aes(xintercept=mean(distance)), linetype="solid", colour="red", size=0.5, show.legend = FALSE)
trimmed_k2_data_hist
Fig3_plots <-ggarrange(Length_Site_Reg, GC_hist, trimmed_k2_data_hist, ncol = 3, widths = 1, heights = 1)
Fig3_plots