Is this sentence a run on a comma slice or a fragment and how would i re write this the correct way After John finished his prewriting, he began his first draft, he was shocked at how easy it was to write the draft since he had planned out his ideas

The sentence is a run on sentence.

The correct way to re-write this would be:

After John finished his prewriting, he began his first draft. He was shocked at how easily it was to write the first draft since he had planned out his ideas.

Explanation:

coin toss of the tosses to the toss

everett ross tried the pasta but liked the soup more