You know what, I was going to run a marathon tomorrow, but online check-in, including a negative test result, two days in advance of the race is the requirement for participation. I didn't check it out at all. It's a shame.

～するつもりだった(意思通りにならなかった)

I was going to...

～するつもりだった(約束義務ができなかった)

I was supposed to...

当選

be selected by the lottery

案内書

Luckly, I've been selected by the lottery for a popular half marathon.

I got the participation guide by post/mail.

But