Are cancer lymph nodes easy to notice on ultrasound? If professional told me not to worry about my hard lymph nodes (i, ii, v region) should I let it go

You are young. Your doctor probably looked at the lymph nodes by ultrasound. If lymph nodes are small enough and have a characteristic appearance then cancer can often be excluded. You're also very young and unlikely to have cancer. However if the nodes persist or certainly if they enlarge they should be looked at again to determine the need for biopsy.
?Hard lymph nodes su. I would be suspicious if the lymph nodes are palpable and are hard when you feel them with your hand. Ultrasound can be a reasonable screen for enlarged and even malignant lymph nodes, but it is not 100% reliable. So if the primary tumor is high risk for metastasis, i would want to surgically remove the lymph nodes for microscopic examination. That is the only 100% reliable test for cancerdetecti.