be a regret

I have a regret.

私は心残りです

I have a regret because it suddenly rained.

私は急に雨が降ったので、心残りです

I have a regret about the outdoor concert I was looking forward to, because it suddenly rained.

私は急に雨が降ったので、楽しみにしていた野外公演を、心残りです

I have a regret about the outdoor concert I was looking forward to with my friend, because it suddenly rained.

私は急に雨が降ったので、楽しみにしていた野外公演を友達と、心残りです

I have a regret because it suddenly rained and my friend and I couldn't see the outdoor concert we were looking forward to right to the end.

私は急に雨が降ったので、楽しみにしていた野外公演を友達と最後まで見られず、心残りです