You got it exactly, but you left out the part about what it means and how it works. Those bonds that have to be redeemed represent money that Congress borrowed and has already spent. To repay these bonds requires higher takes on the 1% (the only ones with any money) or running the printing presses and printing new dollar bills, or borrowing to repay the bonds in the trust with money from selling conventional T-Bills - increasing the deficit.
The fourth alternative is to welsh on the deal. By reducing the amount paid in social security checks by diddling with the cost of living adjustments, the amount that has to be paid back can be reduced without making it obvious that the "full faith and credit" of the US is in the hands of the best congress money can buy.