The task APCAL simply combines the TY and GC tables into a solution table of amplitude correction factors. Your data will almost certainly only include a single frequency band (FREQID=1) and you will want to include calibration data from all antennas for all sources and time ranges.
Use SNPLT to view SN1 and to check that all the information in the antab file has been read by ANTAB and is contained in the SN table. Alternatively, SNPLT can be used to look at the contents of the TY table. You may wish to flag or replace some of the points. Compare the squares of the values in SN1 with those in the EVN status table. If the calibration information is accurate and if the telescopes performed well then the two should agree.