Then don't. As said, flameblade build has way better damage per turn and is also a level 2 spell.
The only good thing about moonbeam is the 100% hit chance. As mentioned, enemies can save against this spell. It's not a true 2d20. It's 5.5 damage for your whole turn (yes, that's right. 5.5 damage a turn at level 5, you can't do a second attack). If you get lucky, you get 10.5 damage a turn. Your only saving grace is an offhand ranged attack, 3.5 extra damage. Excuse me, but moonbeam as meant to be, is trash. Situationally good If it worked, but overall trash. It's near OP at level 2 and then just drops off into the abyss.
Moonbeam is a good alternative to trying to hit something with a ranged attack that will probably miss (ignores AC!). For the druid. That's it. That's the whole point. However, the price is your general damage per turn dropping off horribly.
If the druid had more damage spells than flameblade and that shockspell, it could be alright. As is, you're either a poor tank, a poorer wizard, or perhaps, a terrible paladin. Seriously, the free /cantrip/ from the hag's staff is better than fucking moonbeam. No matter how you play the druid, it's a worse version of some other class. Unless Larian has a sudden power jump planned (looking at you, owlbear!), the class is doomed.