Keep practicing Twinkle Twinkle. Concentrate on the passages that feels uncomfortable or difficult. Try to play it from memory and keep attention to beautiful sound. Practice in front of a mirror in an angle so you can see your bow hand if it is straight (parallel with the bridge). If the bow is in an angle other than that the sound will be affected and not clear.
Read and finish the following exercise:
The music staff and low and high notes - reading