i have just installed the dlc but i have lost my save data and i have to start again :( im using GOG galaxy

What version were you previously using? I had an old version installed and 1.27 seemed to use a different save or path. Launching the older version all my progress was still there. I don't actually own the DLC so I can't check that. I'll see if I can remember to install 1.28 and try that though.

i do not know what version i think the latest before dlc, i had the 2 soundtracks from latest update

I'm using the Linux build. I had forgotten that it saves the progress in the install folder. Checking with PCGamingWiki it appears to do this for all OSes. Hopefully you still have the old install folder with the XML file in it somewhere.