Good job and congradulations, the 2% should be ok. In theory, the old stuff saturates the metal creating a barier to heat transfer and can't be totaly removed without resorting to solvents. In practice, the coolant needs to not boil or freeze, lubricate the moving parts and transfer heat efficiently, all of which it did well before and will do better now.
If you have any nagging doubts, flush it again in one year so you feel good, but 2 years is totaly fine =).