Wow crazy that fuzzybuds called that just on account of the looks and then you say you used cross seeds that weren't stable. That probably has something to do with it.
That combined with flowering them early, and also there's other factors that go into how fast a plant enters full flower like nitrogen levels during the first week of flowering (you want them low or none at all to jumpstart things) and also if your strain is sativa it's going to take longer. But for 4 weeks they should be bigger either way.
I would say there's nothing you can do now, just wait and hopefully it turns out good!