I can't get that page to open, but the title comes up as 'B-2 Stealth Bomber'

Is it an electric B-2 with a 2-channel radio control?

Were there balance instructions? Did you try to follow them? That diving to the side usually indicates a stall, which you can induce by balancing wrong, OR by applying control before the plane has developed flying speed. It is possible you just need to launch it differently. Like, get on a picnic table, and launch it toward the horizon. Or lower. If you launch it with any upward component, gravity will slow the plane. If you launch it toward the ground, gravity will help it pick up speed. If you launch it toward a point below the horizon, the propellor will add speed, and gravity will help it gain flying speed, but it acquires flying speed gradually.

Without knowing any more I won't comment. However, I'm sure someone will.

Good luck,
Dave Olson