I cleaned up something that has been bothering me and I feel great!
I finally took care of something that has been bugging me and I feel refreshed.
I did something that has been bothering me and I feel great now.
「気がかりな」は辞書で調べると「anxious」、「concerned」、「worrying」だけど、この場合はこの重い言葉ではなくていいと思います。
「Something that has been bothering me」または「something that has been bugging me」がいいと思います。「Bugging」は「bothering」の俗語です。
「すっきりした」は「to feel refreshed」か、「to feel great」です。
I cleaned up something that has been bothering me and I feel great!
ずっと気がかりだったことを片付けてすっきりした!
I finally took care of something that has been bugging me and I feel refreshed.
ずっと気がかりだったことをやっとやり終えてすっきりした。
I did something that has been bothering me and I feel great now.
ずっと気がかりだったことをやって、すっきりした。