They keep saying if I don't get that bend I will stay like this as I will get fusion of the knee.
They are wrong. Try to ignore them.
We have had people whose knee has been immobilized in a brace for many weeks and their ROM has increased afterwards, and achieved a good ROM.
At the moment, it's pain and swelling that is preventing your knee from bending. There's no point in hurting your knee by trying to push against that. So stop pushing and spend as much time as you can icing and elevating your leg. That will help to reduce the swelling.
Ice to control pain and swelling
Elevation: the do's and dont's
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.
Your knee has been through a lot and it will need gentle treatment and time to heal at its own pace, not on some pre-conceived one-size-fits-all schedule.
There's no need to rush to get ROM, 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:
Myth busting: the "window of opportunity" in TKR
Been getting a lot of shooting pains along the incision would this be a healing process.?
This might be the zingers we get as our cut nerve endings are trying to reconnect, but it could still be post-surgical pain, too. It's still early days in this new recovery journey and you should probably still be taking pain medication regularly. Are you still doing that?