1. A projection system comprising: a plurality of projectors configured to collectively project an image as a whole on a projection area; memory storing computer-readable instructions; and one or more processors configured to execute the computer-readable instructions such that the one or more processors are configured to, generate correction images including respective correction points which are used for detecting distortions of projection images, which are projected by the respective projectors, based on designated relationships between the projection images of the projectors and the projection area, calculate compensation coefficients, which correspond to the projectors, based on one or more correction captured images that are acquired by capturing the correction images projected on the projection area, generate margin parts in the correction images, which correspond to the projectors that project the projection images in outer areas of the projection area, in a manner so that parts defining the correction points in the correction images are projected within the projection area while the parts defining correction points in the correction images corresponding to the projectors that are next to each other are overlapped, detect an overlapped area between the projection images of the projectors next to each other, one of the projectors being a target projector, and calculate blending coefficients that are used to adjust an overlap between the projection image of the target projector and the projection image of the projector next to the target projector.