Do not be so hard on yourself!! This is great for a first film. You had a lot of very interesting shots and some very intense moments. At least you are self aware enough to know that you have things to improve on. Many people are blind to their own work and think it is the best thing ever created.
I probably wouldn't have noticed the birds, but I guess sfoster made a good point. Although the birds were a great way to create a smooth sound-scape that hid audio imperfections and transitions.
I like the letterbox, but if you choose to crop the image, just make sure you do not crop out the eyes (unless you are intentionally doing that!) It looked like several times the camera drifted too far down and we could not see the actors' whole faces.
And yes about the knife - as a Director/DP myself, I know that many times just because something works well in the script, that doesn't mean it actually works once you film it. That happens all the time. So just try to be honest with yourself when you are on set and answer the question "is this scene working?" If not - then take the time to think it through and re-work it until it makes sense. And ask your actors' opinions too. They will often have good ideas about how to make a scene feel more natural. (but remember you are the director and you have the final say!!)
Overall great work for a first time! Don't be so hard on yourself, and just take what you learned and use it in the next film! Can't wait to see more!
Here are some trailers to a couple films I shot -
I directed, DP'd, and edited this one:
trailer:
https://vimeo.com/93476048
full film:
https://vimeo.com/104404086
I DP'd this one (and edited the trailer but not the film)
https://www.youtube.com/watch?v=yruWbHkvxok