In your situation, I can really see one main problem.
The Air wifi and your trees, keeping LOS for signal.
You can't do much to overcome this, except try and fly high & close, from a high vantage point (you roof ?) and set RTH to at least 150' (if dead sure of your tree tops height, better 200' as suggested.
With tree tops, remember, your RTH will be from take off point, and may be and issue if flying over hilly terrain, so use caution in estimating this, and add that good safety margin.
Recognise the wifi strength meter on your display, and learn how it drops in certain conditions . . . too far, too low with trees starting to block signal etc.
The Air IS very stable in flight, so just check UAV forecast, your tree tops movement, etc, and make sure the wind isn't too high at say 200' to 300', where you'll want to be flying.
From what you post, I feel you need to go and fly some 6 - 10 times (or more) first in a clear open area.
I can't see where you're located, rural or urban, but find a paddock or large sports oval etc, flat with no obstructions, and see what you can do with the Air first with good flight surroundings.
Then expand from there once you feel your confidence grow a little.
I also can't tell from your post if the Air is your first DJI drone or drone of the same level.
If you need to, learn to fly well with turning etc, figure 8's, squares, that sort of thing, you need to practice those and flight first in a good place.
Use beginner mode as you want to be close to learn facing other directions while doing the turns etc.
Also test RTH at the practice location and get confident with that, both using manual RTH button, and a fake disconnect . . . have some foil and with the drone more than say 30m away and 10m up, RTH set say 20m, put foil over controller antenna and block signal, it should disconnect and do its thing.
If you need to, watch some (more) > MAvic Air first flight < tutorials on youtube.
Relax and enjoy your Air, it is a great aircraft.