The gravity of Terra is exactly enough to cause the curved orbit. You are just missing how shallowly curved it really is, by squashing out the time part of spacetime. In 4 dimensional spacetime, the circle is (to simplify a little) really a helix, because it does not return to its starting point, and it's very stretched out along the time axis. (Or very narrow along the space axes, depending from how one choses one's units.) The curvature only looks greater because you are discounting how much greater length of time it extends across in order to do all of that curving that gets it all of the way around Terra.