As you mentioned, you're having difficulty pushing out the high notes at the end. While it's difficult to hear your tone in its completeness (you're singing over your guitar, and it doesn't sound as if your mouth is always aimed at the mic), your tone in your comfortable range sounds pretty good because you don't need a lot of breath support to push the notes out there. When you go up high, make sure you're singing with a strong diaphragm. If you have trouble visualizing this, make sure that when you breath in, your stomach goes out, and when you breath out, your stomach goes in--this "going in" is your diaphragm pushing in on your lungs and controlling the flow of water. Let's say that your torso is a squeeze bottle, like one of those
athletic water bottles. When you turn this kind of water bottle upside down over your mouth, a little water will drip through but not much, because it requires pressure to push the water through the membrane in the top of the bottle and release water. With no pressure, the flow of water is weak. With a lot of pressure (when you squeeze the bottle with the muscles in your hands), the water is going to come flowing out through the membrane strongly, in a clear line. Now, imagine that your torso is the waterbottle (

), and that the cap at the top is your vocal chords, and that your air is the water, and that the flow is your tone. In order for your chords to release
any kind of tone, you need to put pressure on the air in your body to support a strong flow of air, and to direct this air through your vocal chords to create a supported sound. At higher pitches (when the water bottle is less full), it becomes necessary to use even more pressure to reach higher notes. Don't worry about singing loud, at first, just concern yourself with squeezing your diaphragm tightly to support the note. It may not come out as loud as you think it will because a lot of that air will go towards supporting your tone.