Either you have 32-bit Python or you have multiple Python distributions and mixed them together.
For the first case, you could type in the following command to verify.
python -c "import struct;print( 8 * struct.calcsize('P'))"
# The output should be 64.

For the second case, please type in the following commands.
where python
where pip
# A valid output should be like this.
# C:\python37\python.exe
# C:\python37\scripts\pip.exe
# If they don't match, then you could run the command with a specified pip.
# Suppose the output is
# C:\python37\python.exe
# D:\python37\scripts\pip.exe
# Then you can do
# "C:\python37\scripts\pip.exe" install -f https://download.pytorch.org/whl/torch_stable.html torch==1.2.0+cu92