Tinctures are not my top area of expertise and nor is ambergris, however I can tell you two things about alcohol that are relevant:
First drying / evaporating your ethanol may result in water being absorbed from the air as well as ethanol evaporating off.
Second Heating alcohol is very dangerous - the quantity you are talking about probably won’t cause a real problem but ethanol vapour is highly flammable and makes an explosive mixture with air that can be set off by minor sparks such as those caused by switching a light on or off.
Final thought - ambergris is notorious for having very little smell of it’s own, so your tincture may be fine - but also tinctures take a long time - ambergris is normally tinctured for 6 months before use - so you may simply not have given it long enough.
Hope that helps.