Ah, it's a lot easier to help when you state what you want the end result to be :-)
The important thing to note is that MXenes don't consist of a collection of flat layers with a 2-atom basis in a hexagonal lattice (like graphene). So your method to combine different nanosheets will not work.
There are a lot of scientific papers showing the structure of MXenes, even specifically Ti2CO2, such as eg.
https://doi.org/10.1039/C9TA09185H, so I think you would be wise to study the topic more generally,
To build the specific structure you are interested in, I would start with the MAX phase of AlCCr2 which actually is included as a template in the Crystal Builder plugin (under the P63/mmc space group). Just change Cr to Ti and you get Ti2CAl. Once you have built this, remove all atoms except the 3 middle ones (in the Z direction), and you actually end up with the MXene Ti2C.
Now you just have to oxygenate it. My method for this is to select both Ti atoms, and make a duplicate copy of them (menu Edit, Copy and then Paste). The pasted atoms will overlap the original Ti atoms, for now. Change these pasted atoms to oxygen using the Periodic Table button. Then open the Coordinate list and move the two oxygen atoms to the opposite side, respectively. So, the one at z=5.6 goes to z=9 or so, and the one at 7.9 goes to z=4.5 (exact values don't matter for now).
The structure built in this way corresponds to the CBACB stacking in Fig 1 (a) of
https://doi.org/10.1039/c4cp05140h, and making the other versions is straightforward as well, by just shifting one or both oxygen to x=y=0. Note that there is also an alternative structure with ABA stacking for the 3 middle layers, but that is not covered here or in that paper.
Finally, you can use the Quick Optimizer with UFF; the structure I built in this way is attached, and is hopefully a good starting geometry for a proper DFT geometry optimization and further studies.
