My X-rom came today! I found out that its not 512 megabytes.. its 512 megabits!! So.. my X-rom is actually 64 megabytes. :'[
8 megabits (Mb) = 1 megabyte (MB)
There aren’t any GBA blank cartridges that are in megabytes.. they are all megabits. I guess its not that bad because if I got the 256 Mb, I would only have 32 MB.