Stacked bar chart: how to set y-axis properly?

Hi all, I've created a stacked bar chart but the y-axis does not show the correct scale. How can I fix it?
Note I've used a data set in long form using "tidyr" and "gather".
Code:

library(ggplot2)

ggplot(df_long, aes(x = Well_ID, y = Measurement, fill = Analyte)) +
geom_bar(stat = "identity") +
xlab("Well ID") +
ylab("Concentration") +
theme_minimal()

A snapshot of the plot is attached below.

Plot

Stat identity doesn't look right.
Depending on the data use either geom_bar or geom_col, check the documentation.?
If you require specific assistance then please provide a reprex.

Further it may possible your data isn't stored as number but as text.
Please check your dataframe, for example with "str(df_long)".

Matthias, you're right: one of the column was simply stored as character (chr). All solved.
Thank you and Nirgrahamuk for your help and time!