Congratulations on learning to knit!!!
and on trying some colorwork!!!
Your swatch looks great and I think the little issues you mention aren't really issues at all. Because you are working garter stitch you will see one color poke through the other whenever you do a color change. If you were working in stockinette, this would not happen as long as your color change was on the RS row. (note last photo of link below)
The "loopiness" at the ends where you are joing yarns is likely just because these ends are not secured/tightend down. If you don't intend to use the color agian, then just cut the yarn, give it a little tug and weave it in. After washing/blocking it will hardly be noticeable. If you plan to use the color again (a few rows later) then you need to "carry the yarns" up the edge of your project creating a nice neat edge. (see link below)