R ggplot输出和编码

我试图在同一个图上绘制一年内发生的数据，连续三年。我正在使用ggplot（不确定这是否正确），它的缩放效果非常差。我使用的代码和输出已附加

SD192021.plot<-ggplot(data=SD192021.df,
              aes(x=Date, y=AQI.Value, 
color=Year))+
  geom_point(stat="identity",size = 2) +
  theme_classic()+
  ggtitle("Relative Abundance vs Height by 
species")+
  stat_smooth(method="lm", se=F,show.legend = 
F)+
  theme(plot.title = 
element_text(hjust=0.5))+
  labs(x="Height (cm)", y="Relative 
Abundance") + 
  theme(panel.grid.major = element_blank(), 
panel.grid.minor = element_blank(), 
        panel.background = element_blank(), 
axis.line = element_line(colour = "black"),



legend.position="top",legend.text=element_text
    (size=12),
            legend.title=element_text(size=12), 
           axis.text=element_text
    (size=12,colour="black"),
        
axis.title=element_text(size=14),plot.title = 
element_text(face="bold", size=16))
SD192021.plot

SD192021.plot