I'd call this a prayer rather than a spell because this format is requesting a higher power for aid. It's nice and simple, though.
There is one thing I would change, because fire burning paper actually happens really fast. You wouldn't be able to say the full chant, let alone repeat it. Also don't forget safety measures!
Re-written with some commentary, it might go something like this:
Name: Good Luck Coin Blessing
Description: A prayer of good luck to Fortuna, the Roman Goddess of luck.
small, fire-safe bowl
metal coin of value (sentimental or monetary?)
1 piece of paper
lighter (belief isn't an item)
In a well-ventilated area, sit a fire-safe bowl in front of you on a clean and clear surface with no flammable objects around. Wrap your coin in the paper and place it in the bowl. Using a stove lighter (to keep your hands away from the flame), light the paper on fire. Set the lighter down away from the bowl and begin chanting:
"Fortuna, Goddess of Luck, I invoke thee. Hear my prayer and take the offering I present to you. Please grant the good luck I ask of you."
Let the smoke from the bowl clear and wait until the coin is cool enough to touch before picking it up. Blow the ashes (to signify dispersing your request and manifesting your will) and keep the coin on your person.
The only thing I'm iffy on about the re-write is, "Take the offering I present to you." When I work with and worship deities, I come from a place of respect and realize they may or may not actually care about what I'm doing. It feels weird because that line feels like a command more than a request, but ultimately what to do with that line is up to you and whoever else casts this blessing.
If you still want to add in belief as a requirement, you should put that wording into the directions/longer description of the spell.
Ok, i'm ok with the altterattions, its just an idea I thought of, but don't forget that any god or godess will fit the spell/prayer, and I'd keep it as a blessing cus when u offer the god or godess the coin they obtain the energy form of it and u have the physical form of the coin, and ur asking for goodluck, so it's connecting the god or godess with the physical for, of the coin so the person holding the actual coin has goodluck, or more goodluck, depends on the god or godess I geuss.