Rashi: I did not retract from My intent - I brought the evil upon you ¹ ! So I will not retract from the good that I planned to do to you.

Malbim: If you will ask, how can Hashem change from not wanting to wanting - "Lo ka'Yamim Rishonim Ani..." (11)? His will does not change! The verse answers - "Ka'asher Zamamti Lehara Lachem... v'Lo Nichamti." Whenever Hashem makes an evil decree for Yisrael, it is tied to regret. Hashem intends that via the decree, they will repent and fix their ways; then, He will regret and not bring the evil. However, when the evil is for a good purpose - to eradicate Pesha and Chatas, and benefit their end via the evil, He does not regret at the time of the decree. Rather, he decrees absolutely. So I explained "Dibarti Zamosi v'Lo Nichamti" (Yirmeyahu 4:28). When I planned to do evil against your fathers, I did not regret.