I'd consider it unlikely that your system got attacked in any way, but it's not possible to rule out entirely.
Most "spam" e-mails have random looking characters in an attempt to bypass (poorly-implemented) spam filters, but that doesn't immediately mean that it could constitute a threat.
Unless the e-mail itself contained some sort of image (and IIRC Gmail blocks images unless you manually open then) and you saw that image, it's very hard to inject anything malicious into an e-mail, save for maybe a CSS/HTML zero-day (like CVE-2008-2785, CSS), but that seems unlikely. Even so, most browser-based exploits don't tend to work well due to browser sandboxing and other similar security features, although these are still vulnerable to exploit (see CVE-2016-1706).
But let's go down the image route because it's the most likely. Image malware is a fascinating subject, but it really boils down to it being relatively rare because you can only exploit certain versions of a certain program, typically only on a certain operating system. As one can guess, these bugs tend to be fixed alarmingly quickly.
The window for these sorts of attacks is very small, and you were unlikely to be hit by one, if it were present. Due to the nature of these exploits, they can (potentially) be used to break out of the sandbox provided by browsers. For an example as to how something like this can happen, look at CVE-2016-3714 for ImageMagick. Or, specifically for Google Chrome (or, more exactly, libopenjp2), see CVE-2016-8332.
It could be possible that the e-mail you received had a maliciously-crafted image inside it that exploited some bug in the image rendering engine, infecting your machine. This is already pretty unlikely, and if you kept your system up-to-date, you should have nothing to worry. For example, in the case of the OpenJPEG exploit mentioned earlier, any system running version 2.1.2 (released September 28, 2016) would be safe from this exploit.
If you do feel as though you or your system have been infected, it's a good idea to run the standard checks, including clamav, rkhunter, ps -aux, netstat, and good old fashioned log searching. If you really feel your system's been infected, wipe it and start from scratch from a recent known-good backup. Be sure to keep your new system as up-to-date as possible.
But, it's more than likely nothing in this case. E-mails are less attack vectors now as they are junk magnets. If you want, HowToGeek even has an article on the matter that just opening an e-mail usually isn't enough anymore. Or, even, see this SuperUser answer saying the exact same thing.
