What is your rank?

I suggest you fill some more. In case the choices are less and you do not get any college in first round then you won't be considered further.

Whereas somebody who has filled a lot of choices will surely get a college, good/bad doesn't matter but they'll be in the game. You never know maybe with subsequent rounds they even get upgraded to some better college.

Now, if you're rank is really good, say less than 1000 in CET then you're good with 17 choices. But if it's somewhere above 2000–2500 then please be modest and fill more choices, a lot of them.

All the best