I’m not sure what to do in this situation…autistic child and park/other kids

This is a bit of a long read, sorry about that. I’m trying to fit all relevant info in there as summarized as I can.

Backstory — My 4 year old son has not actually been diagnosed yet, we’re still on a wait list for OT, but his pediatrician is pretty certain that he is autistic. We live in a small town and due to the covid lockdowns that started when he was around a year old, waiting until he was almost 3 for the parks and common areas of town to open again, the lack of a need for daycare, and no family members his age until his sister was born, he has had almost zero experience with other children. Now that I’m a SAHM and don’t have work or school responsibilities I am trying to get him exposure to other littles his age as much as possible before school starts in the fall. None of my friends have kids and play groups/trying to schedule playdates aren’t a thing around here because that’s just how the parents are, unfortunately. Our only real option is to take him to the park, and that’s just what we’ve been doing. To be honest I’m scared taking him out in public, especially on my own with his baby sister on my hip. I worry about people judging him. Due to this I try and only take him to the park when there aren’t many people there to warm him up to playing there. He loves going, but he just runs up and down the ramp. He won’t go down the slides without a LOT of encouragement.

Issue — The town’s annual festival is happening this week and we took him to see if he would be interested in going on rides. He wasn’t, so we decided to take him to the park instead. It was busy, but he did great! He actually followed a few kids down the slide and even started calling one of the kids by his name after the boy’s father told my son what his name was. Usually he calls everyone “baby” and doesn’t understand that they have names too.

He asked if we could go to the park again today, so we took him. There weren’t many kids there today but the ones who were appeared to be siblings or cousins and they were around 7 or 8 years old. My husband dropped me and the kids off and went to find a parking spot. My son immediately ran to where the others were, going down one of the larger slides. He started climbing up the steps and got 3/4 of the way there, but he stopped and wouldn’t go down the slide or back down the stairs. The kids started getting frustrated with him and I started getting dirty looks from parents. I had to wait for my husband since I was holding the baby, but I was trying to persuade him to come down during those 5ish minutes. My husband finally got him down and took him over to the main play structure. He didn’t want to go down any slides, just run up and down the ramp. The bigger kids went over to the play structure and my son immediately went to follow them around, my husband had our baby at this point and I was with my son. The kids did not want to play with him and told him to go away. I led my son away from them and told him that the kids did not want to play with him right now, but I would go down slides and play with him. Well we ended up playing with a little tic tac toe board in one of the walls of the structure for a bit. Eventually the kids came back over near us and started using the monkey bars. My husband and I swapped places again and while we were doing that, my son got close to the others and was cheering when they crossed the bars. They seemed okay with that. My son suddenly started freaking out and yelling “no no no” at one of the kids starting to cross. He started pointing towards the slides, wanting the boy to go to the slides with him. I immediately packed up my daughter’s stuff and got her back in the stroller to go over there assuming we would be leaving, which we did. As we were leaving the parents were giving us the dirtiest looks and I could hear the kids talking about how annoying my son was and there was something wrong with him because he seemed like a baby. I explained to my son again that when we go to the park it’s good that he tries to make friends, but if the kids don’t want to play he needs to give them space. I just don’t think he understands. I don’t even really understand what to do. He’s our first, so on top of navigating parenting for the first time with him, we’re also trying to figure out how to approach the fact that he doesn’t really seem to understand things or act the way other kids his age do. What’s the best thing to do in that situation?