How to regain a row of slipped stitches?
When you have a row of slipped stitches that are too tight to fit back onto the original needle, you can pick them up on a different needle, such as:


Use a much smaller knitting needle. Eg, if you knitted originally on US size 8 needles (5.0 mm), use a US size 4 (3.5 mm) or smaller needle to pick the stitches up. The smaller needle should fit easily through the tight stitches. 


If you don't have other sizes of needles, look around your home and see if you have something that could substitute. It just needs to be stiff and skinny. Like a bamboo skewer for cooking.

Use a 16" circular knitting needle. If the stitches are not too tight you can use the same needle size as the original; otherwise use a smaller needle size. Circular knitting needles have a short portion that's the regular thickness of a knitting needle, then a portion of narrow cable. Once the stitches slide over the regular needle onto the cable, you get a little bit of slack because the cable is so much narrower than the needle. (The reason to use a 16" circular needle is that 16" circulars have a shorter portion of regular needle thickness than longer circulars.)
If you don't own a smaller size of needle, use an embroidery needle and scrap yarn. Tie something on the end of the scrap yarn to stop stitches from sliding off. (Lots of things can work for this: a large bead, a pencil, a wristwatch...)
Pass the embroidery needle through each stitch just as if it was a knitting needle. Once all the stitches are safely on the scrap yarn, you can safely transfer them to the original knitting needle. Or if they are extremely tight, transfer them to a knitting needle a size smaller than the original. 


Now that the stitches are all on a knitting needle, them with the original size of needle.

PS: On your next project, work on not knitting so tightly. It takes some practice but it will pay off in the end.