Stretch marks are scars on your skin. They are permanent. You will never get rid of them. My grandmother showed me her stretchmarks from her twin pregnancy 40 years after she'd been pregnant. You can use lotion. You can try to cover them up. But in the end, the best thing to do is learn to live with them.
The purple color will fade eventually and they will be a silvery skin color.
I have stretch marks from my waist to mid calf and have for 20 years.