I have just purchased a Windham Weaponry MPC M4. This is my first "assault" type rifle, so I am brand new to these types of guns. I brought my newly acquired rifle home and read through the manual, disassembled the rifle per instructions (just a basic disassembly, I did not take out every piece and spring), cleaned the barrel and lubed up some of the pieces on the receiver and charging bolt. I put everything back in per instructions; however, I noticed that when the bolt came forward, there was not a complete seal on the chamber/ejection port. I was not sure if this was normal? I am looking to take it out for a test run tomorrow morning, but obviously do not want to damage anything.

Tap the forward assist or let it slam home.

According to the pic you posted that appears to be fully in Battery.    It looks fully forward.   The Bolt Carrier does not travel far enough to close that small opening you see.   Until the parts get broken in it may not go fully into battery easily.   It does require a little spring force to drive in fully into battery generally.   You can check by pressing the "Forward Assist".    What you are looking at is known as the BCG, short for Bolt Carrier Group.   The Bolt fits into the Bolt Carrier.   The Group is all the parts assembled together including bolt, carrier, firing pin, cam pin, firing pin retaining pin, etc.

Also the AR-15 is NOT an "assault" type weapon.    That is a political term designed to make the AR-15 more deadly sounding.   The generally accepted correct term is Modern Sporting Rifle.

That looks like slightly more than I am used to seeing.
Is the BE sticking into the mag well any?

+1. Looks good to me also. The rifle is ready to go in that pic.