Hehe... no you don't need 4 channels... 3 is plenty for an electric car.
You only need 2, I figured I would eventually put a light system in one of mine and need the 3rd channel as a switch to turn it on or off.

I don't really know the GT3 Flysky settings and all... if you have all the programming I talked about in my last post - you're only missing the Gyro and it isn't much to worry about. It's nice to have, but I usually turn it off because it just make it easier to drive the rc in a straight line when you're "offroad" and I like having to do those steering corrections myself.

So don't worry - it looks like a great remote (the GT3 I mean).
If you do have trouble with your order (like banggood being out of stock)... get the RC4G !