It's ok then. you can switch to Mat EI in May. Just call/wirte/fax/go and talk to Service Canada. As long as you have 600 hours in the year ending on your due date minus 8 weeks, you can switch to Mat EI.
Keep in mind, you will not get full Mat+Parent EI (52wks) because you are collecting regular EI before the Mat EI. Total of your regular EI + Mat EI = 52 wks.