Weird! Booting it up, I see no issues with moving. RPG Maker 2003 games can be janky like that, I've had issues with my controls being jumbled in the past, and it just fixed itself after around a day. I have no idea what causes it or how to fix it, but I assume it happens because RM2k3 is over 20 years old now. Try booting it up again and mess with some settings in the F5 menu? That's all I can think of.
Also, thanks for showing interest in my game! I'm working on a sequel to it right now which I think will be much better :D