They might be flexible regarding the deadline. I had recently a similar concern, as I would most probably miss the deadline to visit the Gemeinde. My company suggested me contacting the Gemeinde (Kreisbüro) either via e-mail,telephone or in person to say, without mentioning confusing details, something like the following: "My documents are not complete yet, and as I do not want to hand in an incomplete application for extension, I would need an extension of deadline."

It worked, and they offered me two weeks of extension to hand in my forms and documents. In case you need, you might also try to ask directly for an extension.