I might have a chance at joining a group of players who are all currently 9th level. While roleplaying is fun to me, I wanted to play a character that can deal some good damage or control the battlefield. Problem is, I suck at making strong characters. I don't really care if I play a spellcaster or martial class, but I'm not too interested in playing Warlocks. Anyone got any ideas?

What kind of powerful  are you looking for? The are a lot of different ways to be powerful. Single target damage per round, area of effect damage, buffing, debuffing, area control, nova types, what kind of power are you after?

A focus on single target damage or area control both seem cool.

Wow thats pretty helpful! I don't have a lot of info on the other players, except for the fact that there's some type of Rogue and a Moon Druid, but these seem like good options to consider. Thanks.

Moon Druid is ridiculous early on, but normalizes out after half a dozen levels or so. Now, unless the group really emphasizes optimized combat I really wouldn't worry too much about it - any full casting class with a decent spell selection will be more than fine just doing straightforward control, without needing any sort of shenanigans, so you can go with whatever caster flavour you like best and call it a day - but for a really obvious martial option fighter 5 rogue 4 with Crossbow Expert and Sharpshooter and using Tasha's Steady Aim is an easy to run concept.

I have a Build that can deal about 100 (more or less, depending on the dice) in a single turn, but only once or twice a day, and the second can only be done after a short rest. Basically, it's a Storm sorcerer 5 Fighter 2, tempest cleric 2. Basically, you action surge 2 lightning bolts, and using the divine domain ability and empowered metamagic, (and potentially a bonus action cantrip with quickend metamagic) you can deal alot of damage (minimum of 50) in a single attack, but only if you manage to hit all 2-3, and they don't resist lightning.

Straight Oath of Conquest Paladin.  Great single target damage through Divine Smites, and good battlefield control through Aura of Conquest and Fear type spells.

5 lvs Zealot Barb. + 4 lvs Battlemaster Fighter - V.human Great Weapon Master + Polearm Master

5 lvs Gloomstalker Ranger + 4 Levels Arcane Trickster Rogue - V. Human Shapshooter + Crossbow Expert

4 vs Hexblade Warlock + 5 Vengeance Paladin - V.human Great Weapon Master + Polearm Master

2 lvs Warlock + 7 lvs Sorcerer - Quicken Spell + Agonizing Blast + Hex

For AoE, Draconic Sorcerers or Evocation Wizards tend to do well. I think that Sorcerers can be better at blasting though.

For something that more or less splits the options for your ideas, damage and battlefield control, try something fun and original.

Fighter 6 Bard 3    I say to take Fighter to 6 for extra attack at 5 and he extra ASI at 6.  Battlemaster Fighter gives you a decent ability to do things during combat to adjust the fight a bit, and the base Fighter abilities make sure you're carrying your weight in fights through pure, plain melee damage (or ranged if you prefer, I guess)  Bard gets a great selection of spells to mess with enemies, Lore Bard will be able to Counterspell and Fireball at 6th, or swap one of those for Haste or perhaps Slow for more buffing or debuffing if you prefer.

Another build I've played around with theorycrafting was Eldrich Knight 6 Bladesinger Wizard 3.  Go for Dex as a Fighter instead of Strength, Dueling fighting style and between wearing Studded Leather and Bladesong you get a good AC, you have a decent HP pool from the Fighter levels and both subclasses offer defensive perks to allow you to tank as needed, or use the offensive abilities to really hand out some hurt.  Again, taking the Fighter to 6 gives you an extra ASI to work with, which eases the MAD the build entails.

Fun, not-normal builds that offer a lot of options for both pure damage and some options around controlling the battle.