The email issued mentioned earlier this week is now fixed! You may also have received previous emails that were meant to be sent over the last few days - apologies, this was a one time issue and shouldn't happen again!
Honestly, you can't ask for a much more perfect fit than that. I think you'll be fine, but shoot it and see if it negatively affects your accuracy. If not, roll with it.
I have a 14.5" M4 with a lightweight Mountain Series Rainier Arms barrel in it, and a 15" handguard, and my KeyMo fits JUST inside of it, and if you bump the handguard, you can hear it tap the KeyMo mount inside of it, but it still shoots great, and has for years... So...