Calculating Expenses on Schedule C

I'm a jewelry artist and buy my raw materials in bulk (like stones and metals). I do not keep track of inventory, or assign a value to each individual stone I purchase, so I do not have an efficient way of keeping track of the cost of goods sold, or exact expenses that were actually used. 

 

Can I skip Part III: Cost of Goods Sold, and enter the total of all my purchases as expenses, even if I did not use every single stone or every foot of metal? If I'm understanding correctly, I AM allowed to do this, as long as I don't deduct the cost of any of those materials on future tax forms when I do actually use the material. 

 

Thank you so much for any help, I am totally stressed about this as I want to file my taxes right.