Too long name for online booking?

Hi,

My full name, with all my first names, are more than the 20 character length you mention is maximum on the website.
Is it okay if I just use my spoken name, Henrik, and my last name Karlsson? It will not match my entire name on the passport. On the other hand, if I use my full name perhaps part of my last name isn't printed on the ticket.
Please, advice.

Best regards,

Henrik Karlsson