My COMP1917 exam was done two days ago only and it says the same thing. Though my exam was completely on paper so I highly doubt it was marked that fast.
Just be wary of that. Seems likely that you'll have to wait a while before you can enrol. I guess you could try enrolling every day until results come out. If there's a day before results which you end up enrolling successfully, then possibly that might indicate a fail, otherwise it will keep saying that you passed and then once you see results you'll be fine.
Alternatively, call the CSE and get them to enrol you manually. Just explain the situation and that you want to stay enrolled in it over the summer just in case (I guess they would allow people to do this as a 2 or 3 day gap is pretty short notice to enrol).