This is the 9568th most frequent Japanese word.
縮まっ
"縮まっ" means "shortened" or "shrunk."
The word "縮まる" is in the base form, used to express a wish or expectation about reducing the distance between parties.
彼らの距離が縮まることを願っています。
I hope that their distance gets smaller.
Here, "縮まった" describes the result of the balloon shrinking in size due to it bursting.
風船が破れた後、サイズが縮まった。
After the balloon burst, its size decreased.
The word "縮まっ" here is used in the past tense, indicating a reduction or narrowing of the point difference.