Current Generalized Immittance Converter (CGIC) Nodal Analysis
V4 is connected to more branches than just Y4. It is also connected to Y3 and the output of an amplifier.
Similarly at V3 you didn't account for all the branches connected to the node.
There is node in your circuit that you didn't label with a name or number. In order to get a complete set of nodal equations you need to have an equation for every node in the circuit except one. Typically the node with no equation is the ground node. So you need to add an equation for the unlabeled node.