All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
It is permissible to have an engagement party on the occasion of proposing to marry a girl as long as there is no breaching of the Sharee‘ah (Islamic law) regulations. Some scholars, mainly the Maaliki scholars, are of the opinion that it is recommended to conceal the engagement. There is a Dha‘eef Hadeeth (weak narration) that is given as evidence for this opinion; it states: “Announce marriage and conceal engagement.” [Ad-Daylami: Dha‘eef, Al-Albaani: Dha‘eef]
Hence, the party, in the way that you mentioned, is permissible.
Allaah Knows best.