ether channel will converted physical link in to one logical link then why the loop is not creating in ehterchannel.

Because it's 1 link

Etherchannel while physical is multiple cables for all practical purposes it's 1 connection logicly

go to cisco.com and read up on etherchannel . Almost any question can be answered by searching thru the documents there . Most of their documentation is free and easy to get at .

if I remember correctly, from my BCMSN, STP will use the lowest port id of the bundle to transmit the STP traffic.
STP traffic will not go out all links in the bundle.

Yeah, correct, it will considered as one link. load balanced across the bundle links. so no loop will occur. It will be a loops if the etherchannel configuration accidently removed.

Physically yes
but STP will block one of the ports to stop it from becoming an actual loop

Long time didn't use Cisco switches, did the STP enable by default in the switch?

yep
can't really turn it off
bpdufilter is as close to off as it gets (makes it so the port won't send or receve BPDUs)