I hope the suggested f22 and just a few secs does the trick but I can't help feeling that there is something fundamentally wrong with the strength of the illumination. Is the bulb the right wattage? The alternative is that all the stops on the enlarger lens aren't working. Take the lens out and click it through the range to make sure that it goes from f4 or whatever is the biggest fstop to the smallest.

Assuming that you focus at the biggest fstop for max light are you sure you are then stopping down for the exposure?

No I am not trying to imply you are an idiot but you'd be surprised how easy it is to forget to do things in the early days. I know I have to make sure I stop down each time after focusing and in my haste I have forgotten to do this several times

I hope it all works out OK