Not really, it's the bitrate. 96kbps*60sec*4min = 23040bits, then divide by 8 for bytes, and finally by 1024 for megabytes: 23040/(8*1024) = 2,8mb. I think the issue is that your tracks are too long, try to find a spot where you can cut it off. In Audacity, you can select the last second and use "filter>fade out" to make it loop better. The soundtrack i use for World Domination is 38 seconds, at 64kbps, which gives a size just under 300kb.