These contests are excellent starting points for new mappers. My first suggestion is that your map is extremely open, it looks like people can jump from one area to the end and back. you need to break up the map into little "yards" with multiple passages connecting each yard in sequence. look at other tf2 payload maps, and you will see this. A lot of the time it is done with buildings, but you can also use cliff faces, hill,s etc. Height Variation is your friend!
You're not a noob for admitting that this is your first map and that you are inexperienced.