It would only be too late if you didn't have enough warm days for your crops to mature. Tomatoes take about 70-90 days. Corn takes 90-120 days. You have plenty of time because your first frost won't be until around Nov 1. The warmer the ground the quicker the seeds will sprout and the ground is warmer now than a month ago. Your newly planted seeds will sprout, come on faster and catch up with any that you planted in March.