Wildcard, please...please don't be offended...
You are out in 20kts wind on a sailboat and you don't know the answer to your question....are you not pushing the envelope too much??
Again, please don't be offended, ok?? You really need to read some books or go sailing with someone more experienced.
Answer: Your boat does that because you have too much sail behind the mast. Try this:
1) reef one level on the main
2) Outhaul to the max
3) Back stay to the max
4) halyard to the max
5) Main traveller to leeward max
6) Don't sheet in the main so much
7) get someone that knows about this with you.
Please don't be offended, OK?? not my intention