can u describe more "very instable". if it is oscillatng on z coordonate it is a pid tunning issue. if you have drift on x-y axis it is normal, altitude mode doesnt control it.
it could also be interference on you gps. did you shield your gps/put it far from you camera/ESC. did you try flying in position mode ? in position, the drone should hover and hold position if you leave you rc untouched with sticks in the middle position.
you should concidere adding some damping material under your autopilot, you have to much noise on the accelerometer, but i dont think it is the biggest issue.
pid tunning probably