MOST all "Gaps" fill. They are caused by "retail emotion", and when emotion leaves, the long share holders, bring the stock price back to a reasonable, average new price level.
"Gaps" don't need to fill. They normally do!
90% of all "Gaps" fill !
If you see a "Gap", expect the price to come back and correct the emotion!
A "Gap" is seen, when the day before close price, is lower then the next mornings open price, or vice versa.