how to prevent texture skewness while scaling and rotating

OpenGL OpenGL: Basic Coding
1

Hi everyone
I have just started learning opengl es 2.0. This is my code for setting it up to draw. The problem i am facing is that when i rotate some rectangle, the image gets skewed. the height and width of the texture i am using changes. Can someone tell me what i am doing wrong?

        glViewport(0,0, (GLint)screenWidth, (GLint)screenHeight);

        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();

        glOrthof(-1,1,-1,1,-1,1);
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();

        glPushMatrix();

        glTranslatef(positionX, positionY,0.0f);

        glScalef( -scaleX , -scaleY ,1);

        glRotatef(rotationZ, 0.0f, 0.0f, 1.0f);