You first need to file Form 8606 for 2015 and 2016 to establish the basis in your traditional IRA because you made non-deductible contributions of $2750 and $5500. This will be done in Part I of the form.
You'll then need to amend your 2016 taxes to reflect a taxable Roth conversion. This will be done on Form 8606 also, but in Part II, not Part I. You should have your converted amount ($8730.07 I think) on line 16, your basis of $8250 on line 17, and the taxable amount of $480.07. You will owe ordinary income tax on the gains because it flows back to your form 1040 line 15b.
(Since the above two paragraphs would have you fill out two Form 8606's for 2016, I think it would be more proper to just fill out one form with both Part I filled out to establish your basis for your 2016 contribution and Part II to reflect your Roth conversion in late 2016, and then file it with your amended 2016 tax return.)
You also in theory should amend your 2017 taxes to reflect a taxable Roth conversion to pay ordinary income taxes on the gain of $2.79, but that is so small that while technically correct most people wouldn't bother. If you did so, it would again be Form 8606 Part II. You'll still want to file the Form 8606 so the IRS doesn't think you made a taxable IRA withdrawal.
Same thing for 2018 - you'll need a Form 8606 so the IRS doesn't think you made a $5,497.81 taxable IRA withdrawal. Form 8606, part II.
As for how you filled out the case study spreadsheet, I don't think you did it right. I can't see any reason why you'd have $1389 in C13.
Finally, note that you should get and fill out the Form 8606's for the proper years with the proper year's data - 2015 data on a 2015 Form 8606, etc. The form changes slightly from year to year, and if you put 2016 data on a 2017 form, then the IRS will just get more confused and you'll create more of a mess.