For first time your work is just great.
I can see some little mistakes but they will be gone when you become more experienced braider.
About lace.
If the lace wasn't prepared for braiding good enough it may stretch pretty good. And that stretching problem is a really problem)) because when lace is stretched up, it became narrower, so it covers lesser area.
Button on the left is over tighten and lace became narrower (but maybe it is just low quality of the lace). Button on the right just perfect
Buttons should be thighten firmly.
Looks like body is 6 strand round braid.
It's not a whip it's just a leash so you can pull strings not so tight, just tight enough to hold the core and prevent sliding of the braid.
If in braiding process appears little gaps, and you can't modify your braid (for example from 4 strand to 6 strand, so the strands will cover more arrea and those gaps would be gone), you can hold your starting point and finishin point (or point where you are) of the braid with a thread, and then grab the core and the brain in point where you braiding, and shift the braid towards starting point of the braid relative to the core.
Sorry for my english, hope you would get what I tried to explain.