Finding property boundary in Scotland

I’m on the committee for the winding up of a brass band: location, declining interest, and finally COVID did for us and so we’re now in the process of liquidating the assets using the money to set up a trust to further music in the local area.

Part of the band’s assets includes a large hall and an undetermined area around the hall which was gifted to the band by the neighbouring property some time in the late 19th/early 20th century. Currently the hall sits within an area which is completely walled off on three sides and separated on the fourth side from the original neighbouring property by a fence and tree line. Every plan/drawing we can find though shows the band hall and surrounds as within the boundaries of the original property. Seems like boundaries were never updated with the land registry and the deed in which the hall and land were gifted is very vague. We’re not talking about acres of land here but certainly enough that it would be of great interest to a property developer looking to build a couple of big houses or some kind of low-rise apartment block.

Original property boundary in yellow, current assumed band property in blue.

Anyone have any ideas how we might go about getting an official status on the band’s property boundary?