Not yet, but probably. Let's stop talking about months and use actual dates. When did the child live with you?
You do not claim a dependent for a number of months. You a claim a dependent for all year or you don't claim him at all. The number of months you enter only determines whether you can claim him at all. The actual rule is "more than half the year": 183+ nights, 184+ in a leap year. If there is nobody else trying or wanting to claim the child; you probably don't need to amend.
