The cast on is 19sts and rows 1,2 and 3 maintain that number. You can count the number of yo in row 2 (5 yo) and the number of k2tog (5 k2tog) so the st count should remain the same. Check that you've done all the yo's. You should be able to see them fairly easily on the needle if you tug down on the knitting. It also sometimes helps to go back and look at each st on the needle and check that it corresponds to the chart by naming the sts (yo, knit, k2tog).
In later rows the st count will change, for example row 4 and that's why you see the "no stitch" boxes on the chart.
It's a very good looking belt
which will be lovely. Good luck with it.