Are you doing the milk thing? As gross as it is, it really is SUCH an easy way to get an extra 2400 calories a day for $3...
Don't feel embarassed. Everyone started out there. Once you show that you're dedicated and that you go regularly, I think it's more likely they'll be glad to see you there.
Actually, fail. Doing yoga (or any kind of serious stretching routine) without strength training CAN hurt you.
Flexibility is nothing more than stretching out muscles to allow them to go further. This can be good, but it can also have negative side effects. If all of your shoulder muscles are more flexible, it can destabilize the joint, allowing it to move into positions that could be dangerous.
If you strengthen your muscles as they become more flexible, they will maintain their joint staying-in-place abilities, while also allowing for a greater degree of movement.
and
source:
http://www.cmcrossroads.com/bradapp/docs/rec/stretching/stretching_3.html#SEC26
There easiest way to prevent excess hypertrophy is to stretch after every workout. This elongates the muscle fibers and returns them to their natural lengths. Giant bodybuilder muscles tend to be a result of not stretching and focusing on individual muscles (bicep curls) as opposed to compound lifts (squats).
Look at gymnasts. I would argue that, of all athletes, they are the strongest. Almost all olympic level gymnasts weight train... do you find their bodies gross and unnatural looking?