Help! Minor problems with t shirts!

[buttercup1982]

I've just tried my first t shirt and the square around the design has gone yellow? Have I left the iron on too long?
Thank you!

 

[buttercup1982]

dilemma over! Have fixed it!

 

[Bearnut2]

What was the problem? (just in case someone else has it)

 

[buttercup1982]

I cut a square around the design and the whole part of the square should have been white and it turned out yellow. I have now realised I have to cut around the whole design leaving just a 2-3mm gap. I also think I left the iron on for too long