Yes, it does matter. Etickets are personal and with the wrong name fraud would be very simple.

Correction is not possible, see terms and conditions for etickets When you bought your eticket you have indicated that you had read those so you should be aware.

You cannot correct anything afterwards. Actually the initials do matter as it is a personal ticket. With the initials of e.g. your brothers it is not valid. When the first initial is correct it is mostly ok. The train conductor may ask for your ID or passport to check whether it corresponds or not, but they will not always do.

However, your ticket is illegal in the case it does not match, you may have a fine.