In a large saucepan, combine rose petals, water and lemon juice; bring to a boil. Reduce heat; simmer, uncovered, until petals lose their color. Strain, reserving liquid and discarding petals. Return liquid to the saucepan., Stir in sugar. Bring to a full rolling boil over high heat, stirring constantly. Stir in pectin. Continue to boil 1 minute, stirring constantly. Pour into a jar and cool to room temperature. Cover and refrigerate up to 3 weeks.