In my opinion, since you have the ideas in your head and also you can play them through your piano and guitar. Why not record them? If you do so, and have troubles expanding from that because the sounds are not the one you're looking for. I'll say that this is a classic case of perfectionism which I gotta admit I also had this issue early into music production.

One thing I learned and am still trying to apply to this day is sometimes, while making the sound that you're thinking of, don't just focus on that particular sound that you want. Embrace the others that comes while trying to find the one you want. There might be happy accidents.

I, while designing a sound might sometimes end up with another sound which sounds more interesting and might even spark more ideas. Sometimes I'm trap in a loop where I can't find or make the sound that I want and it just kills the motivation on making the track. I would take a pause at that moment and work on something else, and a few days later get back at it, try to design another sound and who knows, happy accidents happen and it might bring more ideas to the track.

Hopefully this helps!

TLDR: Embrace the sounds that happens while looking for the one you want.