what questions did the officer asked you?
As always the advice is to be prepared for any eventuality given CBSA officers are not consistent.
Some may as previous poster just ask for passport and acceptance letter. Some may or may not ask more if arriving early such how someone plans to support themselves, no way to predict and can be something as simple as how busy they are at the time..
To a degree there is an element of trust that someone is not simply going to break the rules from the outset and is responsible enough to be able to support themselves until classes start... .
.It would likely be very rare if someone was turned away, probably does happen from time to time but more likely due to some misrepresentation being discovered or documentation not in order.
Ultimately goes without saying always answer CBSA questions honestly and you will be fine