Penalty for not filling self assessment

Hello everyone,
Thanks for this forum. It has been very beneficial to me. I remembered I have a penalty why completing my application. A year after I dated my business, I was not paying myself a salary and I didn’t know I still needed to complete a self assessment. I received a fine of £1450. I paid the fine as soon as I got the letter.
I want to declare it but I’m not sure of the category it belongs.
I would be grateful if anyone can advice me on this.
Thanks