Discount code messed up my flat rate shipping cost?

[helloawesome]

Okay, I'm going to try my best to explain my situation in hopes someone has an answer!

I work with Printed Mint as my mug supplier. On their site, they have all their flat rate shipping prices set out. I've used them for years and they're great.

As I setup the flat rate shipping into my shop, I had to account for if someone bought more than one mug. Printed Mint gave me the correct pricing for that. So I set the US Standard Flat Rate as $7.95 and then had to choose a condition based on order price, since weight seemed to not matter in my opinion. I set it to a shipping price of $13.90 for orders that go up to a minimum of $25.98. On paper, it would all work out and I wouldn't lose money on shipping costs...

The one thing I didn't think about was discount codes. All my shipping costs are flat rate and the right amount for multiple products ordered, however, I recently had a customer use a 15% off discount code on an order of two mugs. This brought a loss of -$2.50. 

What do I need to do? I am stumped and not sure how to go about reworking this shipping issue. I'm supposed to relaunch my shop in Feb. Any help would be appreciated! Thanks.