No need for the gym, but eating poorly is a very bad idea.  You need to spend extra effort getting the best food you can get --- whole grains, fruits and vegetables, quality protein.

I am very thing, but still have some excess that makes me feel uncomfortable in dance clothes, or the thought of dancing shirtless. I can't loose it.

We all have things about our bodies we don't like.  Sorry to say, but the only road is to come to terms with it and stop being ashamed with your body as it is.  You probably look great.  So just go dance, shirtless if need be!

i also really want to bulk up. i'll be starting a class in partnering and I don't want to be too weak.

That's less important than you think.  Do 20 pushups every day.  And do them fast, moving from the floor to your arms fully extended as fast as possible (because that's how you must do press lefts).  Then you'll be fine.  Most of partnering is timing and positioning, and most of the lifting is done with your legs (which are plenty strong).

Also my dance belt...I place my penis they way everyone says but I feel so squished and everything tends to shrink...and then making me feel less..impressive. (also it hurts to do exercises laying on your stomach and lifting arms and legs...my weight is right on my penis).

If you don't like wearing a dancebelt, don't do it --- find some other way to provide support that looks neat and presentable in class.  Leotards give good support without the "squish".

And the size of your penis doesn't really matter in life.  It grows and shrinks according to the situation.

Also I am straight, and I don't find guys attractive...except in ballet. Its wierd to me I'm never attracted to guys outside of class...in any degree of undressed or how good shape they are in. But a guy in tights dancebelt and tight shirt turns me on. I don't know what that means...because I wouldn't feel like doing anything with them, but I am still attracted then. is this strange?

It's not strange.  The fact is, almost everyone has some degree of bis**uality.  Most straight men have "gay" thoughts or feelings now and then.  If you just adcknowledge it and move on, knowing who you are, then it's never really a problem.  This stuff only becomes a problem because homos**uality is so TABOO in our society (especially for men) that we freak out whenever we look at a guy and think he looks good, or cute, or something.  So just give it a rest, and chill, and you'll be OK.