Hello, if I made a mistake by filling the wrong information in my application, would it be possible to make changes when I get to TLS office?

Hello everyone, is it advisable to declare previous refusals to Canada in my pre-cas form after already saying I didn't have any visa refusal in my application form because the other schools I applied to refused to grant me offer because of it . I have paid my tuition deposit and I'm scared they might withdraw my offer because of it. Also because pre-cas is related to embassy so I don't know if I should state the refusals there or not or only when I'm submitting visa application.