Cardiac Catherization Iodine Allgery

Hi, my name is Tina and I have a question/problem and would like some advice.  I was having some shortness of breath and went to my primary doctor who did an EKG which was normal. He sent me to a cardioligist since I have a mitrol valve prolapse to have a stress test and echocariagram.  The echo was normal - mitrol valve is mininal. The stress test was positive in a small  area in the front under the breast.  I am an overweight 52 year old female. I was told the test could be a false positive (said 40% of wormen had false positives due to breast tissue).  I am allergic to iodine and shellfish and am so afraid to have the cardiac catherization done.  I dont know whether I should take the chance on not doing it - try to lose weight and maybe repeat the stress test in 6 months or should I go ahead and take the chance.  They say they can pre-medicate me with steroids and benadryl -but I am still terrified.
Can anyone tell me if they have had this test with this allergy and premeds and if it was ok?
Please help - I am scared and dont know what to do!  Thank you for your advice  Tina