Thanks for asking the query,
As you have mentioned that you are having 5 cm gap between your upper and lower teeth i would suggest you to consult the Orthodontist before removal of the braces.
Placement of the retainer after removal of the braces is necessary to avoid the relapse of the treatment, i would advise you to follow the instructions given by the Orthodontist properly.
Maintain a very good oral hygiene
during the treatment.
Hope this helps out.