2 year old tabby, lump on shoulder

I discovered a lump on my (2 year old) cat between her neck and shoulder. It feels hard to me, although I have no real scale to measure this against. When I tried to examine it, she started to bite me, which is atypical for her. Outside of this bump, she isn’t behaving any differently than normal. Her food and water intake is the same, normal energy and play levels.

I took her in for her annual less than a month ago and her blood work was normal other than the sample clotting before it arrived at the lab, leading to an extremely elevated creatinine kinase level (846 U/L). The vet didn’t think it warranted further blood testing. Considering this bump and what I’ve read about what creatinine kinase is related to, it seems like it would be prudent to have another exam and another blood panel.

Is this an overreaction? Do y’all have any recommendations regarding what to ask for with an appointment? I’m not sure how comfortable I feel returning to this vet because of the dismissal of my concerns regarding the lab results.