Application grade error! Help!!!

Hi, looking for some advice / reassurance please.
I’ve applied for Physiotherapy and recently received an unconditional offer from Cardiff University, subject to providing proof of my qualifications. While gathering my certificates to upload as proof, I realised I’d made a genuine mistake on my UCAS application and declared my Chemistry grade as an A instead of the correct grade, which is a B.
I contacted Cardiff admissions immediately to clarify and explain that this was an honest error, as it only came to light during the verification stage.
I’ve also contacted the other universities I applied to, even though I haven’t yet heard back from them regarding interviews or offers, as I wanted to be transparent and avoid any issues further down the line.
Has anyone else been in a similar situation, particularly with healthcare courses or unconditional offers subject to verification? If so, how was it handled? I’m just stressing out right now!