I also was told that if I dont continue to work on this knee it will permanently lock up and they will have to put me under anesthesia and put the knee un place or unlock it so to speak, all of this is starting to freak me out
That's all completely incorrect. They are saying that to try and bully you into working harder, which would be bad for your knee.
There's no need to rush to get ROM (Range of Motion) because it can continue to improve for a year, or even much longer, after a knee replacement. There isn't any deadline you have to meet and your knee is not going to lock up.
Myth busting: the "window of opportunity" in TKR
In any case, it's not exercising that gets you your ROM - it's time. Time to recover, time for swelling and pain to settle, and time to heal. Your knee has the potential to achieve good ROM right from the start, but it's prevented from doing so by swelling and pain. As it heals and the swelling goes down, your ROM (both flexion and extension) will gradually increase, whether you do PT or not
I am noticing that my knee can get so stiff and has been stiff since surgery, is this a problem or is this normal?
That's completely normal. Your knee has been through major surgery that caused a a lot of trauma.
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Your knee is stiff because it's been wounded by the surgery. It needs time and gentle treatment, so it can heal.
The swelling makes it swollen and if you do more than your knee is ready for, the swelling will increase for a while.
Your knee can also get stiff if you keep it still for a while, because while it's still it's not making the fluid that lubricates, rather like putting oil on a rusty hinge.
Finally, stiffness is one other way in which you experience pain.
The stiffness is going to linger for several more months, but it should be decreasing gradually.