Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services immediately if the person:
Elsewhere, contact the local poison information service or emergency number.
And for anyone, someone who:
Contact a poison centre promptly after gasoline is swallowed, even if there are no symptoms.
Do not wait for vomiting or breathing trouble.
Have the container or product name available if possible.
Seek urgent medical assessment after significant fume exposure, repeated vomiting, persistent coughing, chest discomfort, unusual drowsiness, eye pain, blurred vision, or skin blistering.
New breathing symptoms in the hours after swallowing gasoline also need prompt assessment.
The article also says
If someone is unconscious, do not give anything by mouth or induce vomiting.
Move them away from fumes only if it is safe.
Avoid direct gasoline exposure during rescue or first aid.
In the United States, Poison Help can be reached at 1-800-222-1222.
Every sign above is quoted from the sofidex article on Gasoline poisoning. If you are not sure, err upward — it is always reasonable to be checked.