This is exactly what I did too. I filled in the receipt but forgot to put my date of birth ;-( so I sent it once again this morning along with a cover letter.
Hope your application doesn't come back. I am very hopeful that It wil not as all your forms should be complete. They do have a receipt no, and that should suffice but I did not want to take any chances so sent it and would suggest you do the same.
cheers