Hi,
In ijoomla_rss.php file under components\com_ijoomla_rss\
please search for these code:
SELECT * FROM #__content WHERE sectionid=$sec_id AND state=1 ORDER BY created DESC
replace with
SELECT * FROM #__content WHERE sectionid=$sec_id AND state=1 ORDER BY created DESC LIMIT 10
and
SELECT * FROM #__content WHERE catid=$cat_id AND state=1 ORDER BY created DESC
replace with
SELECT * FROM #__content WHERE catid=$cat_id AND state=1 ORDER BY created DESC LIMIT 10
As you can see I added LIMIT 10 at the end, were 10 is the max number of items, you can put another number: 15, 20..