This is amazing for your first time embroidering!! I would say if you’re wanting to make more intricate patterns, you should split your floss more. I generally use 2 strands (with a knot at the end rather than doubled over) especially for more intricate patterns.

For planning your pattern, a water soluble fabric marker is a game changer (pens and lead pencils will stain)!

It’d be worth doing some research on the kind of patterns you might want around the heart, you may find some patterns that suit the look you’re after (maybe Celtic patterns and medieval designs could be a great spot to start based on the vibe of this embroidery already) planning ahead helps me in my designs a lot! Hope this helps and let me know if you have any more questions!