Simple delivery - wrong weight

[energise65]

I have sold an item with simple delivery paid by the buyer. At time of listing I input a weight of 2kg. Halving sold the item and checking the weight, I found it to be 2.4kg. 
clearly my mistake, but I’m not sure how to rectify.
What are my options as I can’t access the postage label to amend it, I can’t buy a correct label and if I cancel the sale I will get a defect.

Any advice would be appreciated 

[thepillenwerfer]

If 2kg was e-Bay's Recommendation it doesn't matter. I've sent several things that have been over weight or size and they've got through fine with no extra been paid by either me of the Buyers.

However if you over-ruled the Recommendation and send it using the label provided you'll end-up getting charged the excess plus £1. 

[xyz307xyz]

I never knew the second bit - is it written anywhere? thanks

[xyz307xyz]

Don't bother replying, thanks! Found it with a web search...

https://www.ebay.co.uk/help/selling/posting-items/setting-postage-options/simple-delivery?id=5575#se...