Turn the safelight off and do another test strip to see if it's a safelight issue. Just do it in the dark.

But the most likely cause is gross overexposure. Stop the lens down to a smaller opening.
And then, instead of doing 5 second intervals, do full stops, meaning 5s, 10s, 20s, 40s. That gives you a better idea of what 'another stop' of exposure in the enlarger means.

Once you got a good test strip, turn the safelight back on to see if you need a new one or not.

Finally, I usually print with developer to about one inch depth in my trays. Keep in mind that you need to agitate the tray. Agitate continuously until the paper stays submerged, and then lift one edge of the tray at something like once every 15 seconds or so. Develop for about two minutes.

Good luck!