Try creating it off of a weapon template such as a javelin
I don't think you will be able to create what you want with a shield. However if you made it a weapon template, then added an AC bonus modifier when equipped, it would essentially function as the weaponized shield that you want.
Rename the text of the javelin to be your shield so it shows up how you want it on your character sheet!
I just ran through it real quick on my phone: When using the javelin template, add Modifier Type: Bonus and Modifier Subtype: Armor Class and you can give it the Fixed Value of 2
To add even further to it: In order to make this truly Captain America's shield, you could create a Weapon Bond like the Eldritch Knight gains access to at the 3rd level
Once you have bonded a weapon to yourself, you can't be disarmed of that weapon unless you are incapacitated. If it is on the same plane of existence, you can summon that weapon as a bonus action on your turn, causing it to teleport instantly to your hand.
So you could essentially throw it as a ranged weapon, have it teleport back into your hand, and still give you the +2 AC for having a shield. It should however be noted that your AC would be -2 once you throw it until it is back into your hand.