You just have to write the 17 first characters of your last name. There is nothing else that you can do.

Then just delete some spaces, or the last letters until you reach 17 signs. Or keep it to one word (e.g. the first word of your last name, people with long composed names do that too in Europe).

No body will make a problem out of it, since this is because of technical limitation.

Btw, best remove your personal details in the screenshot too.

What dates is your travelling?