I am 3.7% Neanderthal (top 99th percentile).
Given that H.S.Sapiens and H. (S.) Neanderthalensis share 98.5% of the genetic material, it would be difficult to be more than 2.5%,or less than 98.5%, depending on how you see it.
What you probably mean is that you have 3.7% of the genetic markers that have so far been identified as being inherited from Neanderthals. Which is a completely different thing from being 3.7% Neanderthal.
I haven't tested my DNA, as there are large privacy concerns with the available testers (none I have found agree to destroying the test and all results except what they send you), but given that I have a large head, big joints, gap behind my wisdom teeth, and hail from where the largest concentration of Neanderthal-inherited DNA is, it wouldn't surprise me if it's up there.
I'm okay with that - it's part of being human.