Class sizes are necessarily limited, often by fire regulations or lab considerations.
CTI is working hard to address this problem, but the numbers alone dictate that this will be a problem for at least the short term. CTI is committed to keeping class size small. Note that there are trains from the loop to other campuses, and that if you have not considered this option, it is definitely worth a look. O'Hare is, e.g., typically 45 minutes away from downtown. Enrolling in another section guarantees that there will be space for you.