You have no, but can try for yes

In Dutch there is the expression "Nee heb je, ja kan je krijgen." This roughly means that being told "no" after asking for something is only as bad as never asking in the first place.

Is there a more convenient English expression for this?

"There's no harm in asking" is a very common phrase

https://www.macmillandictionary.com/dictionary/british/there-s-no-harm-in-doing-something

Also, perhaps when encouraging a timid person, "Go and ask, they can only say no".

Also, "Don't ask, don't get".

Expressions from sports that have passed into common usage (in AmE) include "you miss 100% of the shots you never take" and "you can't score if you don't shoot", the latter perhaps being open to misinterpretation in the context of romantic relationships.