When I run the following chunk of code, I get a very small and unuseful correlation plot(see photo). I think it is because the column labels are too large. Is there any suggestion on how to fix this issue without modifying column names (maybe indicating only substring of names for example...)

numeric.var <- sapply(df_train, is.numeric)
corr.matrix <- cor(df_train[,numeric.var])
corrplot(corr.matrix, main="\n\nCorrelation Plot for Numerical Variables", 
method="number")