Help! Noticed a mistake on submitted citizenship form!

Help!  Tell me I haven't just blown £2K

I have submitted citizenship forms for my kids and noticed that for one of them that I only put in four years worth of addresses, not five as requested.  The full years are in for the other child and both parents.

Can I write a letter to upload with my documents to explain this oversight, or do I need to cancel the whole application, hope the funds are returned, and resubmit?

We are due to do biometrics next week! 

Help!  Tell me I haven't just blown £2K

I have submitted citizenship forms for my kids and noticed that for one of them that I only put in four years worth of addresses, not five as requested.  The full years are in for the other child and both parents.

Can I write a letter to upload with my documents to explain this oversight, or do I need to cancel the whole application, hope the funds are returned, and resubmit?

We are due to do biometrics next week!

I'd just write a note and include it with the other evidence.

Thank you!  After going through the other visa processes previously I'm paranoid about every tiny thing that could go wrong.