Depilatory Cream on bikini line

Hello, does anyone know how to make a perfect straight line when using depilatory cream such as Nair or Sally Hansen on bikini line?

The lines are uneven and I hate that. Using a bikini that I don’t mind being bleached might help, but some of the hair are in between that doing this might not be so great.

Use a towel to cover the area you don’t want to apply the cream on?