I had a swimming class today. This time, I practiced the butterfly stroke. Because I still can't swim the butterfly stroke well, I tensed up and was very clumsy at coordinating my arm and leg movements. Now my stomach muscles are sore😂 今日、スイミング教室がありました。今回はバタフライを練習しました。バタフライはまだあまりうまくできないので、変に力が入ってしまい、手足の動きがぎごちなすぎました。今、腹筋が筋肉痛…😂 "Because ... so... . " this structure does not sound natural. The "so" is unnecessary here. Best to use one or the other but not both "because" and "so" in the same sentence.