Hey i'm taking gcse music (edexcel) as well. Our class are going to a gamelan workshop in two weeks time to hopefully learn more about it and get to play it. But some key words for gamelan are:
Heterophony: Independent melodic lines that interlock with each other in a 'rhythmic combat'.
Slendro: pentatonic scale
Pelog: Heptatonic (seven notes) scale
Gong, Kempur, Kempli, Kemong, Calung, Kendang, Suling: All gamelan instruments
Kotekan: Two-part texture. The left hand plays a basic melody in unison (known as 'polos') and the right hand plays a complex interlocking melodic line (known as 'sangsih').
Also, the key features of gamelan music is lots of repeated ostinati patterns and modulations.
Hope this has helped