Why is your beginning inventory figure "incorrect"? It should be the same figure as your ending inventory from the previous year.
You need to input your ending inventory (most likely the cost of the goods you have on hand). The program will not calculate that figure for you (it will calculate your Cost of Goods Sold, however).
You should know (or be able to reconstruct) how much you paid for material during the tax year and that is the figure that should be entered as the "Cost of Purchases".
Estimates may be necessary but you should note that you may have issues if the IRS ever questions your estimates.
