Depending on where the letter goes that you omitted and where the trip is going, you may not need to change anything.

If just one initial is wrong or missing, no big deal, and if the missing letter makes no real difference to the pronunciation of the name, I also would not worry too much. Johnsson and Johnston would not be in issue for instance nor would John E. Edward or John F. Edwards.

If you fly to the US you definitely need to make the corrections if the family name is spelled incorrectly, but within Europe it all depends, but Ebookers should be able to tell you how significant the mistake is.