I'd suggest going back to square one here. Mix fresh developer, fresh fixer, expose a roll of fim and load the tank. Follow the manufacturer's directions. Pick the time for the developer temperature. Is your thermometer accurate? Agitate for the first 30 seconds. Agitate 5 seconds every thirty seconds after that. Rinse in water. Fix TWICE as long as it takes to clear. You can safely open the tank after a minute in the fix. Agitate it in the fix too. Wash. Now, how do THESE negatives look?
For now, rather than trying to figure out what mistakes you made, or learning how to control the damage, concentrate on learning how to do it correctly from the beginning.
On these forums you'll find all sorts of exotic techniques, like developing with no agitation, using exremely dilute developers, developing in coffee, all fun fun fun, but you need to master the basics first, then it's play time.