Well, somehow I fixed it by resetting the view to default.
Now I can zoom in quite easily and also if I turn the scroll wheel one notch it doesn't jump like 300 meters.
I would also recommend saving your terrain "Raw" height map every so often in case something happens. There is nothing like doing a bunch of sculpting and losing it all, (been there, done that.) Lost 2 hard drives due to hard drive failures in the past year. luckily I had backed up most of everything.