The layout has some issues that are definately causing problems.
All the high current paths that you had are made with 25 mil traces. The trace from the input voltage connector to the capacitors may work, but it's not adviseable. At least the capacitors were tied to the plane. The connection between the MOSFET and the diode is made with a 25 mil trace and then from the diode to the inductor as well. Same is true for the connection to the output connector.
Original Top Layer:
**broken link removed**
The following images show proposed changes to the layout.
*The bottom layer is still a ground plane, but there is a gate trace from the PWM IC to the MOSFET routed in it.
*I got rid of the input voltage plane on the entire top and replaced it with a copper fill that is directed only to the places that require it.
*I flipped over the FET and moved the input caps so that everything is close together with respect to the input rail
*The ground traces for the input and output capacitors were widened and an extra via was added (not really necessary for a 1A design, but it can't hurt)
*The Drain of the FET, the cathode of the diode and the inductor are connected with a large copper fill. The anode of the diode is tied to the ground plane with a fatter trace and two vias.
*The inductor, output capacitors and output connector are tied together with a large copper fill.
*The feedback path is connected right at the output connector pin.
*I removed R5 and moved R4 to be between the VFB pin and Ground.
*Comensation components were rearranged cuz I'm anal
Top Layer Edit:
**broken link removed**
Bottom Layer Edit:
**broken link removed**
Since the max output current is only 1A, the MOSFET and diode are way oversized. This could be done with smaller packaged components and the layout could be compressed to make the board much smaller.