DC power supply is capping out at around 3amps and 3.1v for powering my electromagnet
There are two obvious problems.

1) Unless you are using a logic-level FET, 3.3 volts is not enough to reliably turn on the FET.

2) At the same time, opening the switch will not reliably let the FET turn off. The gate is floating (being neither pulled up or down), so the state of the FET is not defined.

Both of these issues can be addressed with a small change:







simulate this circuit &ndash; Schematic created using CircuitLab

When the switch is closed, the gate is pulled up to 9 volts, which should provide adequate gate drive. When the switch is open, R1 will pull the gate to ground.