You will need to file the Schedule C to report any income received, including whatever 1099-MISC you receive.  You can deduct the website fees, $100 starter fee and any other related expenses as business expenses on that Schedule C.  And you do not have to keep an inventory to file a Schedule C.   When you get to the question about inventory, just answer NO.  This article should be helpful to you - Beginner's Tax Guide for the Self-Employed

you do not have to keep an inventory to file a Schedule C

True. But the fact is based on your statement, you were given 7 bags to sell and you paid $100 for those 7 bags. That comes out to $14.28 that you paid for each bag. So if you sold one and (your words) "made $10", that means you sold it for $24,28 or more and made a profit on that particular sale. You still have 6 more bags in inventory that you need to account for.

I would suggest you "cover your basis" and report the inventory. You'll indicate you sold one, and that the rest were removed from the business "for personal use" That will leave your end-of-year business inventory at zero. Then so long as you have no other assets or business vehicle use, you won't need to bother with SCH C on your 2020 tax return next year.

If you actually do receive a 1099-MISC, the income paid to you will be reported in box 7. As far as the IRS is concerned, income reported in that box is self-employment income.

Overall though, you may not receive a 1099-MISC. The issuer of that form is only required to issue one to you, if they paid you more than $600 in a tax year. So in your case, you may not even get one.

With the petty amount of money you're talking about here, were I in your shoes and didn't receive a 1099-MISC I wouldn't bother reporting anything on a SCH C at all. A mere $100 expense on your part "might" make a $1 difference in your tax liability (if that much) and reporting it on a SCH C isn't worth my time.