You are making the Amish Friendship bread you forgot to add the ingredients on day 6 Will this mess up the recipe?
Yes, you can use it the next day.
A sourdough starter is used to make this bread. Provided that
you look after your sourdough starter, feed it, and keep it growing
in the conditions it likes, then there is no reason why this one
starter can not be used again and again and again. Some people have
starters they made themselves, and they are over 15 years old.
With a sourdough starter, the flavour can change over time,
reflecting the yeasts that are in your home. If your started
develops a taste you don't like then you may want to create a new
starter.
http://www.sourdoughhome.com/startingastarter.html - will give
you more information on how to create a sourdough starter.