Usually that means there's no result, which can have several reasons, one of which is indeed sold out. Your screenshot is to small to be able to read. What is the train you're trying to book (origin, destination, date, departure time)?

It’s Prague to krakow july 13 at 10 am. Not sure if it’s because I bought first class. Or if tickets are sold out? Or if i shouldn’t worry yet? 

The train is still not open for bookings Usually it should be 60days in advance however some Internationaltrains in Poland can be booked just 30days in advance :/

I recommend to check regulary on https://www.cd.cz/en/default.htm if the train is open for bookings (This way you save the booking fee of Eurail ) Just select under the big green button the option “I want a reservation only”

Thank you. And do you know. If I bought a first class ticket May I reserve a seat in second class for the one leg when I’m travelling with others ( who have second class passes)? 

It is no problem to sit in 2nd class if you have a 1st class pass.