Yes, you've coded this incorrectly. If you'll review your CPT code descriptor for 11901, you'll see that this code is for '8 or more' lesions, not for 'each 8' lesions. CPT 11900 is assigned when fewer than 8 lesions are treated; 11901 when more than 8 lesions are treated.
If your provider has documented that the treatment of 35 lesions involved significantly more work or time than normally involved when treating more than 8 lesions in a single encounter, then you might consider appending modifier 22 to code and requesting additional reimbursement from the payer. However, I'd caution that I think it's unlikely that a payer would allow additional payment because 11901 is already valued to reimburse work across typical provider encounters which may involve different number of lesions. In other words, your provider is being paid a per-visit rate, not a per-lesion rate, for this type of service.