Recognising it
Scope creep is rarely one big request. It is eleven small ones, each individually reasonable, that together add a week.
What we do
Track them. When the accumulated total becomes material, we raise it as a single conversation with a clear choice: extend the date, drop something else, or approve the extra.
What we do not do
Silently absorb it until quality or the date suffers, then explain afterwards.
Your part
If something matters more than something else in the original list, say so. Trading is much easier than adding.