Here is the small Trendy CC with the dimensions. It's a beautiful bag.
The bags out now for 24C are the new mini size with the rainbow letters.
Chanel also makes variations of the classic Trendy CC that includes more or a cut sparkly CC/raised gold letters.
I personally prefer the classic version.
As you look at Trendy CCs, note that Chanel seems to alternate the release of Trendy CC and Coco Handle each season.
The current season, 24C, focuses on the mini Trendy CC. This means next season, the focus will be on the Coco Handle. That seems to be the trend, but of course, it's not a given.
If you are looking for the basic black color, you can just ask your SA to reserve one for you when they come in as black is an often repeated color.
Note also on the Coco Handle, some seasonal versions have a "gold chain" stitched to the top of the handle. For me, it's a bit loud.
I don't mind the CC logo, but I am not a fan of all that extra added gold.
Finally...
Since you are new to Chanel bags... I need to mentioned the all metal chain. I hate the classic chain... it digs into my shoulders!
I'm small, and I seem to have boney shoulders and collarbone. This also means that I cannot wear that metal chain strap long term as it digs into my shoulders. Yes, I can wear a mini crossbody for a short period such as running errands, but I can't wear it longer, say, walking the city streets for a day. It just digs into my shoulders/rubs my collarbone. Then, I have to keep adjusting and moving it, which then defeats the purpose of a comfy crossbody bag.
It's getting cool now, so people are wearing thicker clothes. Try on a chain bag in summer/light clothes, and see if it bugs you. You may be fine, but just FYI. And try it on with your stuff inside, not empty. This may not be an issue to you, but FYI as it would be a waste of money to buy that bag only to be annoyed when wearing it.
For me, whe I buy Chanel bags that have chains, I only buy ones that have the leather strip in the center of the chain. I need that for comfort. Both the Coco Handle and Trendy CC have that leather strip.
I think it's a wise decision to return the bag you bought. I don't think you'll love it after a season or two (it will look screaming logo loud as well as a bit dated).
Good luck to you! Buying Chanel is super fun. No need to rush. Work with your SA to ask her what's coming out next season, and you can get on the list for the bag you want.