Your data and model correspond to the example on the help page:
http://xxm.times.uh.edu/learn-xxm/latent-growth-curve-model/
Please take a look at the data for the example. Here is the key change you would need to make:
The first column must be IDs for the specific level (‘response’). In your case, the first column is a predictor. Create a new column called ‘response’. Each row of ‘response’ will be a unique integer value. ‘response’ will also be the the name of the first level. Doing so allows xxM to link data from the ‘response’ level to student level data.
hope this helps.