Had cough a month went to hospital I blew in a peak flow meter then got a neb treatment and tolled me I had asthma how would I know for sure if I do?

Diagnosis... By definition, asthma is recurrent episodes of bronchospasm so you need more than one episode for the diagnosis to be made. You can also have pulmonary function testing to determine if you have any bronchospasm either at rest or with provocation testing. See your doctor so you can be diagnosed and treated, if you have asthma.
Complete evaluation. A fair definition of asthma is wheezing that gets better with albuterol - the stuff in the nebulizer. To confirm the diagnosis see an allergist or pulmonologist to take a complete history & perform an examination & lung function & allergy testing. If you have asthma it's important to investigate causes & severity, understand outcome & begin appropriate treatment.
Asthma. You would benefit from another physical exam and a spirometry test. This involves breathing into a computer measurement device that can analyze lung function. Many primary care offices have these available, or a pulmonologist or allergist will definitely be able to help.