Did you pre-drill holes before trying to screw them in.

If you used a screw meant for metal, that might be the problem.
Pre-drilling is important too. Deck screws are meant for wood and their other screws that for wood as well.

ugh..didn't know you had to drill the holes before you screwed the screws in.

Thanks for responding.

I am going to do better next time!

You can also use a little dry soap to help the screw. Just run the screw across a bar of soap, it doesn't need to be completely covered. Good luck.

Two inch wide board would be better to last thru the weather. Pine doesn't have the staying power as much as cedar.
Also screwing them thru braces at the corners would make them nice and firm.
Like the braces on my coldframe cover shown here.

quiltbea, thank you...pictures help! so this will be a cover for the bed in case of a frost?

Yes, cherry63, I lay this plastic-covered frame over the coldframe during the nights until it warms up a lot. It can also help warm up the soil before planting anything if I cover the coldframe during the day for a week or more.