I'm hoping to spend one day by myself and the other two days with my friends and girfriend.
I'd like to relax by myself for one day and spend some time with my girlfriend and friends the other two days.
ーI'm hoping to spend one day by myself and the other two days with my friends and girlfriend.
「１日は自分一人で過ごして、他の２日は友達と彼女と過ごそうと思っています」
to spend one day by myself で「１日を自分一人で過ごす」
to spend the other two days with ... で「他の２日を…と過ごす」
ーI'd like to relax by myself for one day and spend some time with my girlfriend and friends the other two days.
「１日は自分一人でリラックスして、残りの２日は彼女と友達と時間を過ごしたい」
to relax by myself で「自分一人でリラックスする」
to spend some time with ... で「…と時間を過ごす」
ご参考まで！
I'll spend one day by myself and the other two days with my friends or girlfriend.
「過ごす」は英語で spend を使うのが一般的です。
「一人で過ごす」は spend time by myself または spend a day alone などと言えます。
I'll spend one day by myself and the other two days with my friends or girlfriend.
『一日は一人で過ごして、残りの二日は友達か彼女と過ごす予定です。』
カナダ 
アメリカ合衆国 
