Your ROM is good for your stage of recovery. Really, it is! And it's entirely possible you will have 120 flexion at 3 months. But if you don't... that's okay, too. I can't imagine a surgeon would take a knee with 100+ flexion and want to subject it to an MUA. It makes more sense to give that knee more time. Your knees will continue to gain ROM for months still, even after a year. Being patient with them, especially with your already good flexion and extension, is sensible!
Being diligent about exercises will not give you more flexion. But there is one thing that will: reducing your swelling and inflammation. Those angry, swollen internal soft tissue
physically block your knee from bending. They take up space and prevent bend, not much different from the way a hose filled with water is tough to bend.
In a normal, non-injured knee, these soft tissues are efficient and sleek and fit amazingly into their small space. But when your surgical, still-healing knee is aggravated and inflamed, that space remains the same size but the soft tissues swell... that's why irritating your new knee early on is such a negative. The swelling hurts; it hampers function (and hurts more when pushed); and it slows down healing.
So, yes, you already nailed that you were a bit too active the other day. At eight weeks, I could walk around the grocery store without much problem, but a college campus? I wince just thinking about it. And given the above explanation about the connection between flexion and swelling... yes, that kind of thing impacts your flexion. Mine could easily go up and down 5 degrees depending on whether or not I'd had PT the day before (down the day after PT, and up when measured again at the next PT).

And it only went up, never down, after I quit PT.
So don't worry about your flexion. It's there. It'll show itself when the swelling inside your knees goes down. You're having a really good recovery, so pace yourself.
