Tydings Park, head straight out, cross the susky channel and look for four to seven foot water depth and start fishing. Perryville is good if you plan to fish carpenters point but I have had my best Spring luck out ot Tydings.
I think Tydings Park in Havre de Grace is currently closed for an upgrade. Perryville Community Park is a good spot but has time restriction with gates. Opens around 7:00am-7:30am and closes promptly at "official sunset". And when I say closes, the gate is closed and locked regardless if there are still cars inside.
Check out the MD-DNR site and click on their Boat Launch Atlas. Then click on either Harford County or Cecil County for specific information. Also click in the Havre de Grace insert for more kayak launch sites. BTW, some of these cartop only launches are real bears to launch from. So look them over first when you are not in a hurry to launch.
I launched out of Tydings last season around this time of year, but it sounds like its closed. If you are able to launch out of Tidings, I'd watch the current and the wind. I head directly east after leaving the marina, the wind picked up to the east and I had a heck of a time paddling back, had to paddle for 90 minutes straight fighting wind and waves that the winds kicked up doh. My recommendation would be to paddle upstream towards the railroad bridge and let the current take you back.