It does sound like this is your first rodeo.
You should never even use the top three cogs when you are in your big ring. (Unless you have a double and a straight block)
All my Mtn bikes are set up with the chain too short to even get onto the top two cogs when I am on the big ring.
You need to use the gear combinations that give you the best chain lines and access to the best jumps from the middle ring.