Wa'alaikumassalam sis! Egg white mucus like that boleh jadi sign labour is coming, tapi tak semestinya hari ni or tomorrow, some mums keluar macam tu for days before actual labour starts. Since you're already past 39 weeks by scan, best you call your gynae or go to labour ward to check, especially kalau ada contraction or other symptoms like bleeding or fluid leak. A few of my mum friends tanya doctor pasal ni and they all got checked out just to be safe, better tenang hati, kan? Keep monitoring and jangan hesitate to go in if anything feels different or you're worried.