How Taxation Works on Owner Finance Flip with Note Sale

[Adam Nonnenmacher]

In 2019 I bought a house, and flipped with owner financing. Since flipping qualifies you as a "dealer", you cannot qualify for an installment sale which means I have to pay gains tax all at once even though I am taking payments.  

How taxes would look according to IRS as a flip
Cost basis: 20,000
Sales price: 34,5000
2019 Taxable income: 14,500

How I feel like taxes should look if I actually made 3k in 2019 and 3k in 2020
Cost basis: 20,000
Sales price: 34,500
2019 down payment: 3,000
Carried note for: 31,500
2020 Note sales price: 23,000 (3k profit)
2019 down payment + 2020 profit from note sale = 6k

So how is this handled? Do I pay tax on the entire $14,500 from the sale in 2019 (according to IRS) or just 3,000 down payment as profit (I assume down payment is pure profit and not a reduction of basis?) then pay the tax on 3,000 from note sale in 2021... this is so confusing to me.