My deezer is synced to last.fm but it wont show my songs on the last.fm web

Currently the internal Deezer scrobbling option is lagging again, so it is several hours behind your current listening with submitting the scrobbles to your Last.fm account. And it does not provide the “Scrobbling now” track info in your Last.fm recent track list anyhow, so it might look as if it does not work at all.

I guess you are on a free account at the moment, did connecting to your Last.fm account work on the Sharing Preferences page in the Deezer web player, so that the Last.fm logo is in red there?

Also note that depending on your device for Deezer listening you could also use external scrobbling apps like the Web Scrobbler browser extension or Android scrobbling apps like Pano Scrobbler which has a Windows and Linux desktop version now.