in the display of your DataSource (RSA1 > DataSources > <select your DataSource & double-click it>) follow menu path: Goto > Technical Attributes
in the PSA Properties block you'll find the (real) PSA table (in the form of /BIC/B*** where *** stands for a bunch of numbers)
double-click it
here you can see all the requests that are still in your PSA
if you want to selectively delete from this table, create an ABAP program for it
otherwise empty the table via process chain with process variant Delete PSA request (set older than date to 31.12.9999) or use SE14 (if you know what you're doing)