What an adorable little boy you have there!

I agree w/ Wolf_Q when she says not to take everything to heart and to keep up w/ the class and socialization.

However, Pit Bulls are one of the breeds that can be dog agressive and by owning a pit mix you should be well aware of that. Being human agressive is something that's NOT natural so it's great that he loves people.
My pit, Smokey, isn't dog agressive - so far. I had him in puppy class at 10 weeks and he was just great and it helped SO much with being able to take him to the park and occassionaly let him off leash. (Only when the other dog owners are well aware of what can happen, but know Smokey and encourage me to let him off leash because he's such a sweety.)

What am I trying to say here?
Keep up w/ the classes & socialization but understand w/ this breed there is a chance you won't be able to let him off leash or take him where there are lots of strange dogs. It's important to note that sometimes dogs do not show their full aggression potential until 18 months of age.

Just be aware of your dog and those around you and you should be just fine.

Good luck!

P.S. PLEASE DON'T PASS HIM OFF AS A BOXER MIX!!
Don't be ashamed if he has some dog agression, it is natural. It's just how you handle it that will make the difference (But in general, unprovoked human aggression is NOT natural AT ALL for the "pit bull" breed)