If you have registered TM in single class, you will get protection in that class alone. You cannot get protection for all the classes. If you want to protect your TM in other Classes also you can file Application for those Classes. You can file multi class Applications on class 99. Or which ever class you need you can file in that class.
Ipr Lawyer(Trademarks Patents Designs and Copyrights)
Well the views expressed above are right. However if you just missed appying in the other classes but your trademarks is an invented mark or a coined word like "ONIDA" OR "SANSUI". you can assert your right under common law of Passing off. However, in any case you shall apply for the registration of your tm in other classes also if you wish to protect the same under the Statuory law.