1.020 raises other questions because it depends on how you are making wort and which yeast youre using.
If you are AG and using liquid yeast, you should oxygenate somehow. This could be your problem.
If you are AG and using dry yeast, you dont need to add oxygen. Some people shake the fermenter (bit hard at 60L) and others insist no oxygen is required at all. Even some manufacturers state no oxygen needed. Theyve packed everything into their dried yeast it needs. My previous batch was 50L with 3 packets of US-05, rehydrated and it got to 1.012, no oxygen, no shaking. Great beer. Here it is, unfiltered.
If using dry though, youll need enough yeast and rehydration is a good idea.
If you dont have enough yeast, that could be your problem.
If you do have enough dried yeast, try rehydrating first.
If AG and using a lot of crystal malt and/or mashing high (temps) this can cause a high FG
If using kits and enough rehydrated yeast, pretty much thats how it will be.