Schedule C "Life Coaching" Limited square fotage box has an input of 300. It keeps telling me to change it? 300 sf is the maximum allowed.

in put is 300 sf

When you use a portion of your home for your business, you will need to enter the total square footage of your home and the square footage of the area you use as your home office.  There are two methods to use to figure your home office deduction. An Actual method and a Simplified method.  The Simplified method limits your home office square footage to 300 sq ft at $5.00 a sq ft.  If your office is larger than 300 feet, you can enter that, but if you choose the Simplified Method for your deduction, TurboTax will limit it to 300 square feet. 

Hope this helps!