It's a shame I took the whole day off school today and all I've done is sleep.
I missed a whole day of school today and I have spent most of it in bed.
この場合、次のように言うのが自然かと思います。
ーIt's a shame I took the whole day off school today and all I've done is sleep.
「せっかく今日1日学校休んだのに、寝てただけだよ」
to take the whole day off school で「学校を丸一日休む」
all I've done is ... で「やったことといえば、…だけだよ」
ーI missed a whole day of school today and I have spent most of it in bed.
「今日は学校を丸一日休んで、ベッドでほとんどを過ごしたよ」
to miss a whole day of school で「丸一日学校を休む」
to spend most of it in bed で「ベッドでほとんどを過ごす」
ご参考まで！
カナダ 
