you can reduce the data size by lowering the bitrate. while 320kbps is great, in most cases 128-192kbps will be fine and the drop in quality will be barely noticable. keep in mind also that fl studio (assuming that is what you are using) seems to over estimate the final size of mp3 files by 1-3mb
that being said, this definitely needs some remastering before 3:58 but you have something going. one of the components of each of your buildups seems to have a lot of very intense white noise in it. IMHO it is a little too intense. I also think that be bass needs something is a few places, perhaps just a little more stereo offset on the delay.
that being said, it is a great start. plenty of variation while maintaining a repetitiveness that makes it easy to add into a long set. also a great selection of samples.