That depends on whether it makes sense to you to seek protection in that class. If you were to succeed and secure the trademark, you'd only be able to exercise your rights in the new class. Also, you have to be able to qualify for registration in the said class with the goods/services your brand offers.
Other than that, your options will depend on the situation, e.g. your jurisdiction, the likelihood of the brand coming forward, the nature and degree of the similarity, etc., and we would therefore recommend discussing your next steps with an attorney.
It's worth pointing out that even if a similar brand decides the oppose your application, you might still have options to save your trademark. We've detailed them in the article What happens if someone opposes my trademark application? In the end, your decision will depend on your ability to accept risk.