Missing middle name in ILR set(M) app - cover letter or resubmit?

Hi all, I've made one of those silly mistakes with my Set(M) ILR application - submitted it, paid fees and booked a biometrics appointment for the end of this month, only to realise that in the "Given names" field I've missed out my middle name so it's not shown anywhere on the application! My residence permit doesn't expire until 10 Oct, so I assume my options are:
1) Attach a cover letter to the supporting docs to explain that I've missed out my middle name in the application form
2) Withdraw the application and apply again with the correct information

Obviously I would prefer to go with 1), but I'd love to know if, based on your experience, this is a sufficiently big error to merit 2)?

Any advice would be much appreciated!

A cover letter is enough.

Super, thank you for the quick response Zimba!