Ok...not a bad effort but I think it could be improved. You did a good job of using trunks of varying thickness and heights!
I would encourage you to look at the distance between your trunks. Use a chop stick to measure and compare the distances between the trunks and I think you will find that many are very close to the same distance apart. It may not appear to be so evenly spaced from the "front" view but when looked at from multiple points there does seem to be very even spacing. In my opinion, it is a mistake to build a forest from a single point front view...I like to call this a photo front or 2D front..
Outside of photos, which is the worst way to view bonsai, we NEVER view a group composition from a single stationary point. Instead we are constantly moving our heads/eyes and changing our physical positions to observe compositions...thus giving ourselves a 3d perspective. IMO, group plantings should be designed with this perspective in mind. One thing that can help is having at least some of the trunks very close together. Clumps of 2 and 3 trees together can also help over come this very common spacing issue.
Again IMO your container is much larger than it needs to be...you could certainly use something two thirds, or maybe even half the length and width of the current tub. I would also encourage you to use some much shallower... Group compositions always look best in shallower containers...there is no better time than when you create the group to begin working on making it more shallow. BC are tough and can handle severe root reduction when done at the appropriate time.
Only trying to help you build better group plantings!!