Did I mess up my first retainer?

I'm a new level 52 bard. I had a retainer from an early level that I used for just storing stuff but recently when I got into crafting, I decided to make my retainer a gatherer. So in doing so, did I lose any levels that retainer had as I leveled up my bard? I read today that I was supposed to make my first retainer a DoW retainer. So if I have made the retainer a botany gatherer, have I now lost the opportunity to switch her back and make her a DoW? Do now what happens? The DoW retainer has to level herself up? Thanks in advance.

They reset their levels anytime you change their class/job. Making them the same as your main class just means you can gear them easier as you can just throw your older equipment onto them. That and they'll level better as you'll be gaining levels while going through the msq and thus they won't hit a cap until you reach max level. While on the other hand a DoL will need you to have spent time leveling that out as you don't have as many ways to level that vs a DoW retainer. You can switch their class/jobs at any time as long as they're not out on a mission. Not sure if you can change them if you haven't completed the mission. You also have access to two free retainers so you could keep one as the gather and the other as a DoW.

You level up retainers by sending them out on ventures. The maximum level for a retainer is your own level in the class/job the retainer has. Any time you change the class of a retainer it will lose all progress in its old class.

The general advice to give your first retainer the same class as your own main DoW/DoM class is because that way the retainer will not be limited in level more than necessary, and you can easily outfit with the gear you no longer need.
Other than max level and ease of gearing them, it does not matter at all which DoW/DoM class/job you give your retainer.

If you are leveling Miner and/or Botanist on your own character, it is often worthwhile to make your second retainer a Miner or Botanist.
Should you ever pay for a thrid retainer it should usually be the missing one of Miner/Botanist/your main class.

If you were previously just using your retainer to store stuff and not for ventures, then he/she didn't have any levels to lose, since it's ventures that give your retainers XP. They don't level just because you are.

My advice, leave the retainer you've set to Botanist as a Botanist, but get a second retainer (you'll want another retainer's worth of storage space as you get into crafting anyway) and make that one your Bard retainer. Send them both out on ventures to level them up until they catch up to you in level. (The longer 18 hour exploration ventures in particular give a lot of XP.)

They won't be able to exceed your level in their respective classes, though. Nor in the targeted hunting/mining/botany/fishing ventures will they be able to gather items you haven't gathered yourself first (though in exploration ventures they can). So there's an extra incentive to be sure you gather each item in your gathering log at least once.