I just had some great racing on MRc Beginner FBM but I forgot to save replay, is there a way to get it now? or is it forever lost

If you left server,did not join other server and did not close LFS,the latest mpr is still in your mprs list as temp_mpr - run it or rename it for storage. If joined other server or LFS was closed,then only way to get is to contact server owner (or whoever has access to server's control panel),then it can be retrieved from it,assuming mpr auto save is activated.

Quote from Eclipsed :

If you left server,did not join other server and did not close LFS,the latest...

problem is that another race has started before i could hit 2 to save mpr. I did manage to get my hands on it as another player did save it

Great

You can enable autosave of all replays, but that is a hassle on its own as depending on your activity your disc usage can grow dramatically over the time.