Hi, Aquamarine Deer

You don't worry about what has past.  Consider this moment in time.  Since you are starting mid-month consider it your runway to your official first full month, March.  Look at what you have in funds right now and assign those funds to budget categories.  Do you need to use what you have in the bank right now to pay March rent? If yes, budget it to rent. Do you need to do another grocery store run between now and your next salary deposit? If yes, make sure to reserve enough money to buy food.

I too started in the middle of a month, August 2014. When I pull my reports, I exclude August 2014 because it does not have an entire month's worth of expenses.

Check out some basic getting starting steps here

https://support.youneedabudget.com/category/quick-start

And consider joining a free online class

https://www.youneedabudget.com/classes/

I started in the middle of the month and only included my current bank balance at that time and any pending transactions. 

Aquamarine Deer

I also started in the middle of the month; November 15th to be exact. I ran into a "spending freefall" on the 2nd of November when the sewer water backed up in my bathroom. I ended spending money here and money there to get it fixed. Had my savings account connected to ynab. I kept transferring money and I had it all messed up.....so I started a new budget on December 1st; I keep doing the workshops and now things seem to have fallen into place. I put my income into the category "To Be Budgeted" when I receive the money.  Do some of the workshops....they really helped me.