Contradictory information on CPU-usage on EC2 t2.micro

Hello community.
I am using EC2, to be more specific a t2.micro virtual machine with Amazon Linux as OS. I noticed some performance issues so I checked RAM- and CPU-usage. In case of RAM the AWS instance monitoring wouldn't give me any information, but using the Linux command "top" the VM (virtual machine) showed very low RAM-usage, so it should be fine. The issue with the CPU turned out to be more complicated, since the AWS instance monitoring showed me usage of up to 12.5% (= 1/8), whereas the VM itself reported 100%, again using the Linux command "top". Further the VM reports having 1 CPU without specifying wether it is a processor, a core or a vCPU.
It would be very important to know which value is the correct one for coming up with a solution for the performance issues. Does anyone have an idea?
It would also be interesting to know how this gap came to be. I was thinking about a quad core processor having 8 vCPUs and the AWS monitor showing me the whole processor (which I cannot use), while the VM takes the vCPU as maximum, but that would be kind of silly.
Thanks for your ideas.