you're only calculating the effect of gravity over 1/30th of a second for each step - you need to do it cumulatively. Step 1 should end with a velocity of 0.09G, Step 2 with .18G, step3 with .27G etc.
Here's a very simple example that draws the ballistic trajectory based on start velocity and a supplied time:
using UnityEngine;
using System.Collections;
public class grav : MonoBehaviour {
public Vector3 StartVelocity;
public float PredictionTime;
private Vector3 G;
void OnDrawGizmos()
{
if (G == Vector3.zero)
{
// a hacky way of making sure this gets initialized in editor too...
// this assumes 60 samples / sec
G = new Vector3(0,-9.8f,0) / 360f;
}
Vector3 momentum = StartVelocity;
Vector3 pos = gameObject.transform.position;
Vector3 last = gameObject.transform.position;
for (int i = 0; i < (int) (PredictionTime * 60); i++)
{
momentum += G;
pos += momentum;
Gizmos.DrawLine(last, pos);
last = pos;
}
}
}
In you version you'd want draw your dots where I'm drawing the Gizmo, but it's the same idea unless I'm misunderstanding your problem.