Hi Liou
this has some nice atmosphere. When it comes to the second chord, you are correct that you want the note to be in relation to that chord (this is how your ear will interpret it anyway). You don’t need to use a C minor scale necessarily. C minor will differ from G major in having the notes of Eb and Bb – Bb sounds tense against G major as it is the minor third of G. You probably want to avoid that – in the example above, your ‘featured’ notes sound atmospheric, but that minor third against the G major chord sounds a bit less deliberate and it might be harder to make that level of tension work.
Keeping it simple is excellent at this stage. We really want to hear what the shape of the melody is. Imagine if someone was singing this and you’ll be along the right lines.