My floor buckled i took out four plank 2 1/4 when i installed the new one
i have a gap i can't get the last one to fit i measured the old againt the new same size what could be the problem am i lay it in wrong or what

Many times when a floor "buckles", that is due to moisture causing the wood to expand. When you took out those 2&1/4" boards, the space that they came from is most likely slighly smaller (less than 2&1/4") The simple remedy to trim the new boards to the size of the space. Trim on the groove side. If taking off very little, a hand plane will work. If you need to remove a lot of wood, you will need a table saw. There is also a particular way to re-install T&G flooring. One needs to remove the bottom of the groove on the one side and slide the new floor board into place by inserting the tongue first at an angle, then rotating the board down into place. It's easy when you know how but tricky if you've never done it.

Thanks for the reply i was considering trimimg the board i was not sure if this would help i was going to try a reverse clamp and spread the gap it apart slowly each day should i try this before i trim the board i am looking at a 6' feet section to run also if trimmed will the grove side have to be re- done as well you say cut the button groove off then insert the tongue in and rotate it?

That's the reason the floor buckled. It gained moisture and swelled. Now the wood is taking up more area then it once was.

Your reverse clamp idea, will only buckle the floor elsewhere.

get yourself some dental floss and lay it in the hole before you set the board in .. if its two high and you need to cut more of the bottom grove off , you will be able to get the board out without dammage to the other boards ..

On 3/4" solids the face side is a little wider than the board bottom. Flip it upside down to check the fit. When you rip the bottom groove off set the table saw to a 5-10 degree bevel allowing you to back cut a little.
If the face side is too wide sand the edge with a palm sander until she drops in.