Do I Have Marfan's?

I have a question about Marfan's syndrome. I've always been tall and skinny. I am 5'11, about 145lbs, 29 years old. I've never had any major heart issues other than an occasional palpitations. I had a pneumothorax about 10 yrs ago, which hasn't reoccured. I have a negative thumb sign (which means my thumb does not extend beyond my clenched fist) but a near-positive wrist sign. My arm span is 6'2, my actual height is 5'11 1/2. However, my armspan to height ratio is only 1.03, under the 1.05 limit people say for Marfan's. I do have long arms and somewhat spidery fingers. I had an echocardiogram 2 years ago and it came back normal. I do look tall and thin, but My doctor thought I might just have characteristics of Marfans and not have the actual disorder. Might this be the case? Do I have Marfan's or just symptoms of it. Like I said, no major heart problems ever in my life up to now. Thanks to whoever might give me clarity.