In 10 days, a 13 week old puppy is very unlikely to know what you want.
You need to put in the effort to teach him.
Hold a favorite toy in your hands. Talk to the toy, turn it over looking at it. When puppy tries to take the toy, ignore puppy. AS SOON AS puppy sits, give him the toy and praise him. Repeat often. As puppy starts sitting quickly, add the word "sit" - hold the toy and talk to the toy and turnit over looking at it; when puppy comes over, say "sit", as soon as puppy sits, give him the toy and praise him. Repeat often. Now start asking him to sit for other things - treats, before going outside, putting on his leash, etc. Always praise him when he sits. He'll catch on quickly.
Most likely right now, you are telling him to sit as an end to his fun. He's playing with the ball and you tell him to sit so you can take the ball away from him. In YOUR mind, you are doing it so you can throw the ball again. In HIS mind, you are taking away his toy.
You want to teach him that your taking the ball doesn't mean an end to the fun. Using the process above, you're going to add a step. When he has a toy, simply take hold of an end. Don't pull on it or fight for it. Just hold it and say "let me see it". At some point, he will loosen his grip to get a better hold. At that time, pull it away from it calmly. Hold the toy up and talk to it and turn it over looking at it. As soon as he sits, give it back and praise him.
Dogs are like kids, they want you to want what they have - but they don't want you to take it away. You are using the above game to teach him that you love his toy but won't take it away. As you repeat the game, he will start to bring his toys to you to see - because he knows you will give them back when he asks politely (sits).
With ball playing, many dogs never enjoy fetching. They want to chase the ball, but don't want to give it back. You can try offering him a treat for giving up the ball. You can play the "let me see it" game above. You can get a second ball and when he comes close with the first ball, throw the second ball. When he goes to get the second ball, pick up the first ball. Repeat.
You don't want to grab for the ball. This becomes a game of keep away for the dog. And it's a fun game for them.
My own Tornado-dog will play "go ahead, try to take it" with me as much as we play fetch. I'll throw the ball, he'll go get it and bring it back, then he spends several minutes dropping it in front of me and grabbing it back if I try to pick it up. It's a fun game. I just wait patiently until he decides he's ready for me to throw the ball again. Sometimes he does that just so he can catch his breath before continuing the fetch game. As fetch is a game, not a job, I don't stress that he doesn't do it exactly "right" each time. As long as he's having fun, we play it his way.