Passion Pink Cordyline problem

K1mbrad

Please could anyone help, I am new to gardening?

 I brought a passion pink cordyline approximately 6 weeks ago, it is currently outside in front of our shed in a pot. 

I put a protective frost proof bag over it and as the sun has been out uncovered it to find it no so pink, looks very unhealthy and has yellow spots.

Please could anyone tell me what I should do before I loose this plant

Many thanks