Can I modify my order after submitting?

Need clarification on the signature field. Should my signature:
1. Match my real signature?
2. Be neat and legible or can it be messy?
3. Include my full name or just initials?

Also, does the signature need to match the name on the ID exactly? I usually use a shortened version of my signature in real life.

Don't want to mess this up. Thanks for any guidance!