why is the compound non aromatic despite it having resonance? 

Having resonance doesn't mean something is aromatic, you also have to have a fully conjugated system. Have you drawn out the resonance structures? 

Look here at the 'four rules'

https://www.masterorganicchemistry.com/2017/03/03/is-this-molecule-aromatic-some-practice-problems/
 

Quote

Our last post in this series on aromaticity went through the 4 conditions a molecule must fulfill in order to be aromatic.

• First, it must be cyclic
• Second, every atom around the ring must have an available p-orbital
• Third, the number of electrons in the pi system must be 2, 6, 10, 14, 18, or a higher number in the set that increases from 18 in increments of 4 (22, 26, 30…. etc). We usually abbreviate this as [4n+2] pi electrons.
• Fourth, the molecule must be flat.

In that post we tried to explain what each of those rules meant – so if any of these individual items seem unclear to you, it might be a good idea to go back to that post.

In this post,we’re going to apply these 4 rules with some practice examples.

Look down the examples to cyclobutene (could you name your compound ? )

Can you find a cyclobutene that is aromatic?