Step 5: Pouring
You only need to pour to the level you wish the LED to be fixated at. If you just dropped it in, it would sink to the bottom which in this case is the top of the soap, looking rubbish. Leave to set hard before placing the LED on top.
If you want to, you could add colouring to this project and have two different colours. I prefer transparent though. Don't use food dye - it stains.
If you've heated the soap too high it will get bubbles in the mix - avoid at all costs. If like me you get this, you can explain that like normal hearts it is not pure red, but has layers of white fat to protect and encase the electrical nerve impulses... (yeah...)