Error in Database

Hello

My code is

Use DBInMemoryOLTP
Go
ALTER DATABASE DBInMemoryOLTP ADD FILEGROUP [DBInMemoryOLTP_data] 
CONTAINS MEMORY_OPTIMIZED_DATA
GO
ALTER DATABASE DBInMemoryOLTP ADD FILE 
( 
NAME = [DBInMemoryOLTP_FG1], 
FILENAME = 'c:\database\DBInMemoryOLTP_FG1'
) TO FILEGROUP [DBInMemoryOLTP_data]
GO
ALTER DATABASE DBInMemoryOLTP ADD FILE 
(
NAME = [DBInMemoryOLTP_FG2], 
FILENAME = 'c:\database\DBInMemoryOLTP_FG2'
) TO FILEGROUP [DBInMemoryOLTP_data] 
GO

Error message

Msg 10797, Level 15, State 2, Line 27
Only one MEMORY_OPTIMIZED_DATA filegroup is allowed per database.
Msg 5170, Level 16, State 2, Line 36
Cannot create file 'c:\database\DBInMemoryOLTP_FG2' because it already exists. Change the file path or the file name, and retry the operation.