The installation directory could not be configured

[shorile]

CentOS7.4 n2n version2.8

I typed this

./configure -h

See the appropriate help message like this

By default, `make install' will install all the files in
`/usr/local/bin', `/usr/local/lib' etc.  You can specify
an installation prefix other than `/usr/local' using `--prefix',
for instance `--prefix=$HOME'.

then typed

./configure --prefix=/opt/n2n make install

Prompt compilation successful

BUT, They are all in the default directory，nothing here in /opt

Did I make a mistake?