Don't open the notes application. It will use the autosave
file and everything else will be lost.
You could try this:
open xterm and enter:
cat /home/user/.osso/osso-notes/.g_keyfile

The output should be something like this:
[notes]
window_count=1
active_window=0

[window_0]
is_current=true
current_name_exists=false
current_folder_exists=true
current_folder=/home/user/MyDocs/.documents
filename_exists=true
filename=file:/home/user/MyDocs/.documents/Hello.note.html
autosave_filenames_exist=true
filename_autosave=file:/home/user/.osso/osso-notes/autosave.0-Notizen.note.html
filename_autosave_no_ext=file:/home/user/.osso/osso-notes/autosave.0-Notizen
file_format=1
alignment=0
strikethrough=false
text_position=0
edited=true
fullscreen=false
cursor_offset=12
bold=false
underline=false
italic=false
bulleted=false
text_colour_red=0
text_colour_green=0
text_colour_blue=0
font_face=Sans
font_size=3

Maybe the file at the "file=..." entry isn't overwritten yet and
your notes aren't lost. If this file exists:
1. make a backup/copy
2. open the file from the file manager

hope this helps

nicolai