I got that same Jagermech as my first heavy, too! It’s kind of hard to make it work - the default loadout is only good if you just love doing chip damage from a distance. I ended up turning mine into a front-line tank with one AC/20, a couple small lasers, jump jets, and a whole lot of armor. It’s beefy enough to tank a number of hits, and doesn’t need any heat sinks.
If you have a Gunnery pilot with Breaching Shot, the AC/20 will wreck everything at this stage of the game, guarded or not. If that same pilot has Bulwark from the Guts tree, you can just jump jet into close range, then stand still and blast everything without worrying about having to move.
There are much better mechs for this kind of build, of course, and when you start facing off against heavies regularly it’ll be outclassed. But early on, I definitely want one AC/20 in my lance, and this is the first mech you have that can realistically field one!