IK this will confuse you more, but actually, officially, internationally recognized and standardized, you are correct and 1GB = 1000MB = 1000,000,000 B.
Still most people use 1GB for 1024 MBs. Officially, the 1024-based unit system contains a small 'i' before the 'B': thus 1 GiB = 1024 MiB...