You might be able to sit on the stone part around the flowerbeds in the rotary in front of the station. However, since it's not very high, it might feel like you're sitting on the ground.
As a side note, Marugame Castle, one of the remaining 12 original castles, is located about a 10-minute walk from Marugame Station. The small castle tower perched atop the high stone walls is quite a sight to behold.