Mars is not Earth
On Earth, continents are the result of plate tectonics.
We KNOW that Mars has never had plate tectonics, since it first formed a stable surface, so we don't expect continents.
As for liquid water, yes, there probably was liquid water at that sort of time, but not permanently. It would be temporary thing - every time a giant impact occurred, ice would vaporise ionto a steam cloud, then rain out. it would last a little while (decades to 10,000 years?) before freezong again.