Yes. I was able to get the COM3 connected. How do I check my sketch is uploaded?
If you disconnect the Uno, does COM3 disappear? If so, you have the correct port.
The IDE will tell you if the sketch is successfully uploaded. Further you can test by uploading e.g. blink; if you think it works, modify the timing of blink (e.g. three seconds on, one second off) and upload again; is the change reflected.
If Serial is working, how can I see what I send through Loopback activity?
Open serial monitor and type something; it should be echoed when you click the send button.
On Device Manager, it does not say anywhere Arduino. It says USB Serial port as COM3.
If it's not an Uno with 16U2, device manager will not know that it's an Uno and hence not say that it's an Uno. For a clone without 16U2, USB serial port sounds right.