I shot using raw/jpg for all the pictures. I moved on to the next picture in the strip but it only had the one picture it was missing the jpg
There is a Preference setting on the General tab-

If this is checked then Lightroom-Classic will import BOTH the raw and its JPG pair (sidecar file) into the Catalog, and should show them both on the Filmstrip.
If you do not see both, then the possibilities are-
-There was no JPG to import,
-The JPG was not Imported, (See the Preference setting)
-You deleted the JPG (from the Catalog & possibly the drive),
-You have a Filter active that only shows the raw files.
-You are viewing a Collection that does not contain the JPGs
tried removing the rest of the pictures from Lightroom
WRONG, WRONG. Lightroom-Classsic uses a database (Catalog) that references the images you add into the Catalog. [Remove] them from the Catalog- then they will not show, and if you chose [Delete from Disk] then they are totally gone (to the trash).
Import ALL photos to the Catalog- That is the prime purpose of its existance! to make a Library index of your photos (then its secondary purpose is rendering raws & developing images).
I selected the folder that the pictures were in but I only checked the ones I wanted and left the rest unchecked.
What do you mean by "checked"? (Selected, Flagged, placed in a Collection, filtered?)
in Lightroom there are JPGs missing on 2 or 3 pictures and I don't know how to get them in there.
If they are not in the Catalog (or were removed) -Import them once again (Presuming you did not delete them!).
You can do this (Import) in either of two ways-
1) Use the normal [Import] dialog with the [ADD] option set and select the folder (in a File Explorer window) where they are stored in the Source panel, or
2) you can select the Folder (where you know they exist) in the Folders Panel and [Right-Click] and select [Synchronize Folder...]
If you are not understanding the basics of Catalogs then start with this free eBook for Lightroom-CLASSIC from the Lightroom Queen-
https://www.lightroomqueen.com/