Some of your ECs may be done during school year. Summer positions are harder to get into. Everybody’s situation in this respect is different, do whatever you could in your specific environment. The benefits of long term internship at your college is that it may result in great LOR from the person in charge of the Research lab.
And keep in mind that all As are the goal, but first, do not get discouraged if it does mot happen and second, all As are still no guarantee that certain Med. School will invite you to interview. Some will still reject or ignore your application. So, applying widely and staying cool are the only appropriate options for you at the end. That is if you have enough of everything to apply.