My puppy got aggressive with me?

DO NOT PUT A MUZZLE ON A PUPPY!

your puppy is acting like a normal puppy.

buy a dog pen, it will keep her out of mischief when she's older, and the pen will help with the biting issue.

when she bites you, say no in a stern voice and leave the dog pen for a few minutes. she'll realize that biting=no more play, if you're playing with her out of the dog pen and she bites you, say no in a stern voice and put her in the dog pen! you can also put a toy in her mouth everytime she tries to bite you

always praise her when she's playing with her toys, also take her for short walks during the day to release some of her energy.

Dump the muzzle.If you are in the habit of muzzling her, using this will make her aggressive. She is too young for long walks, however she can have several short walks a day. You can also play train her in your safe fenced garden/yard. By doing the above, she will be calm and happy.

The problem is a "pit mutt"

That's what happens when you have a vicious dog for a pet. And get used to it and be ready for more bites.

For now, TRADE the toy for a treat. Most dogs have to drop a toy to take a treat. While I do not like that she bite you, I do not recommend direct confrontations. (Did you yelp or hollar to let her KNOW it hurt?)

I would WORK on her giving up a lesser-liked item like a plastic or metal dumbell or a large ball (that is hard for her to hold tightly).(Most dogs aren't excited about obedience dumbells - they are used primarly for obedience). You teach the dog "Take IT" (place item in the dog's mouth - if needed) Praise! Then teach "Give" - where the item comes back out. Plan to give a treat for all "gives".

I would also enroll the puppy in a formal puppy obedience class, ASAP. You need to be more in control, than you are.