Those marks run the long way (assuming it's 35mm, which would fit with your 300 ml developer volume). That pretty much means they got there when you hung the film to dry, which means they're most likely due to mismeasuring your wetting agent for the final rinse. Too much wetting agent can leave a residue that dries on the film, rather than running off cleanly, and the resulting marks will look much like what you see there.
Fortunately, wetting agent residue is usually easy to fix. Just rewash the film, and treat it with the correct ratio of wetting agent to water before hanging it back up to dry.
In my experience, fixer doesn't leave flow-like marks, and if your film had touched between turns on the reel, you'd have huge blotches of undeveloped and unfixed halide visible where the liquids were kept away from the emulsion. Fixer that's only its very last legs can leave density variations, but they'll usually be more like developer flow marks, which would be vertical in the tank orientation (not aligned along the film).