I have had 2 knee replacements. I allowed them to push me to do aggressive physical therapy the first time, and the second time, I did not. I recovered a lot faster the second time.
You don't say what angle you can bend to, and how straight you get your leg. Your surgeon will advise you if you need surgical intervention.
19 times a day with the heel slide? No wonder you cannot raise your foot higher. Stretching ends up weakening the muscles, so the non-stretching exercises are for strength, and the stretch exercises are to increase range of motion, but the ROM stretches decrease strength for a while after stretching.
The stretch I was shown this time was much less difficult than the one I had the first time. This is from my PT the second time around. Sit on the edge of a straight chair. Move the toe of the surgical leg back behind the edge of the chair. You can pull on your pants leg. The heel does not stay on the ground. Rest the ball of your foot on the ground until the foot gets far enough back to rest the toe of your shoe/sneaker.
My cousin was a lot stiffer than I was after her 2 knee replacements. Her surgeon told her that you cannot get more ROM than you had before surgery. A lot of people's ROM decreases a little from what it was before surgery.
I agree with everyone: a swollen leg cannot be bent as far. Because I had swelling, it made bending very difficult the first month for me. (I am 7 1/2 months). To address the swelling: elevate above your heart while sitting and in bed. Do not dangle your feet while seated. Walk every hour. Ice, ice, ice. I used an inflatable triangle pillow on the footrest of my recliner, plus a pillow on top of that. I used an "ice machine", which my surgeon told me can be used 24/7 when seated or in bed. Be sure to wrap your knee with a king size pillow case to protect the skin, but an ice machine never reaches freezing temps. because it is water, not ice. Walk more day by day. Getting your blood to circulate will help move out the excess fluid. I was very worried for a while because I thought I might get lymphodema in the leg.